1,2

See A000032 for the version beginning 2, 1, 3, 4, 7, ...

Also called Schoute's accessory series (see Jean, 1984). - N. J. A. Sloane, Jun 08 2011

L(n) is the number of matchings in a cycle on n vertices: L(4)=7 because the matchings in a square with edges a, b, c, d (labeled consecutively) are the empty set, a, b, c, d, ac and bd. - Emeric Deutsch, Jun 18 2001

This comment covers a family of sequences which satisfy a recurrence of the form a(n) = a(n-1) + a(n-m), with a(n) = 1 for n = 1...m - 1, a(m) = m + 1. The generating function is (x + m*x^m)/(1 - x - x^m). Also a(n) = 1 + n*sum(binomial(n - 1-(m - 1)*i, i - 1)/i, i = 1..n/m). This gives the number of ways to cover (without overlapping) a ring lattice (or necklace) of n sites with molecules that are m sites wide. Special cases: m = 2: A000204, m = 3: A001609, m = 4: A014097, m = 5: A058368, m = 6: A058367, m = 7: A058366, m = 8: A058365, m = 9: A058364.

L(n) is the number of points of period n in the golden mean shift. The number of orbits of length n in the golden mean shift is given by the n-th term of the sequence A006206. - Thomas Ward, Mar 13 2001

Row sums of A029635 are 1, 1, 3, 4, 7, ... - Paul Barry, Jan 30 2005

a(n) counts circular n-bit strings with no repeated 1's. E.g., for a(5): 00000 00001 00010 00100 00101 01000 01001 01010 10000 10010 10100. Note #{0...} = fib(n+1), #{1...} = fib(n-1), #{000..., 001..., 100...} = a(n-1), #{010..., 101...} = a(n-2). - Len Smiley, Oct 14 2001

Row sums of the triangle in A182579. - Reinhard Zumkeller, May 07 2012

If p is prime then L(p) == 1 mod p. L(2^k) == -1 mod 2^(k+1) for k = 0,1,2,.. - Thomas Ordowski, Sep 25 2013

Satisfies Benford's law [Brown-Duncan, 1970; Berger-Hill, 2017] - N. J. A. Sloane, Feb 08 2017

P. Bachmann, Niedere Zahlentheorie (1902, 1910), reprinted Chelsea, NY, 1968, vol. 2, p. 69.

L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 46.

Leonhard Euler, Introductio in analysin infinitorum (1748), sections 216 and 229.

G. Everest, A. van der Poorten, I. Shparlinski and T. Ward, Recurrence Sequences, Amer. Math. Soc., 2003; see esp. p. 255.

G. H. Hardy and E. M. Wright, An Introduction to the Theory of Numbers. 3rd ed., Oxford Univ. Press, 1954, p. 148.

Silvia Heubach and Toufik Mansour, Combinatorics of Compositions and Words, CRC Press, 2010.

V. E. Hoggatt, Jr., Fibonacci and Lucas Numbers. Houghton, Boston, MA, 1969.

R. V. Jean, Mathematical Approach to Pattern and Form in Plant Growth, Wiley, 1984. See p. 5. - N. J. A. Sloane, Jun 08 2011

Thomas Koshy, "Fibonacci and Lucas Numbers with Applications", John Wiley and Sons, 2001.

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

S. Vajda, Fibonacci and Lucas numbers and the Golden Section, Ellis Horwood Ltd., Chichester, 1989.

Indranil Ghosh, Table of n, a(n) for n = 1..4780 (terms 1..500 computed by N. J. A. Sloane)

Mohammad K. Azarian, Identities Involving Lucas or Fibonacci and Lucas Numbers as Binomial Sums, International Journal of Contemporary Mathematical Sciences, Vol. 7, No. 45, 2012, pp. 2221-2227.

Arno Berger and Theodore P. Hill, What is Benford's Law?, Notices, Amer. Math. Soc., 64:2 (2017), 132-134.

J. Brown and R. L. Duncan, Modulo one uniform distribution of the sequence of logarithms of certain recursive sequences, Fibonacci Quarterly 8 (1970) 482-486.

Enrico Di Cera and Yong Kong, Theory of multivalent binding in one and two-dimensional lattices, Biophysical Chemistry, Vol. 61 (1996), pp. 107-124.

G. Everest, A. J. van der Poorten, Y. Puri and T. Ward, Integer Sequences and Periodic Points, Journal of Integer Sequences, Vol. 5 (2002), Article 02.2.3

Sergio Falcon, On The Generating Functions of the Powers of the K-Fibonacci Numbers, Scholars Journal of Engineering and Technology (SJET), 2014; 2 (4C):669-675.

Scott Garrabrant and Igor Pak, Counting with irrational tiles, arXiv:1407.8222 [math.CO], 2014.

R. K. Guy, The strong law of small numbers. Amer. Math. Monthly 95 (1988), no. 8, 697-712. [Annotated scanned copy]

Sarah H. Holliday and Takao Komatsu, On the Sum of Reciprocal Generalized Fibonacci Numbers, Integers. Volume 11, Issue 4, Pages 441-455.

R. Jovanovic, First 70 Lucas numbers

Blair Kelly, Factorizations of Lucas numbers

Tanya Khovanova, Recursive Sequences

Clark Kimberling, Matrix Transformations of Integer Sequences, J. Integer Seqs., Vol. 6, 2003.

Ron Knott, The Lucas Numbers in Pascal's Triangle.

Kantaphon Kuhapatanakul, On the Sums of Reciprocal Generalized Fibonacci Numbers, J. Int. Seq. 16 (2013) #13.7.1.

D. H. Lehmer, On Stern's Diatomic Series, Amer. Math. Monthly 36(1) 1929, pp. 59-67. [Annotated and corrected scanned copy]

Edouard Lucas, The Theory of Simply Periodic Numerical Functions, Fibonacci Association, 1969. English translation of article "Théorie des Fonctions Numériques Simplement Périodiques, I", Amer. J. Math., 1 (1878), 184-240.

Mathilde Noual, Dynamics in parallel of double Boolean automata circuits, arXiv:1011.3930 [cs.DM], 2010. - N. J. A. Sloane, Jul 07 2012

Mathilde Noual, Dynamics of Circuits and Intersecting Circuits, in Language and Automata Theory and Applications, Lecture Notes in Computer Science, 2012, Volume 7183/2012, 433-444. - N. J. A. Sloane, Jul 07 2012

Simon Plouffe, Approximations de séries génératrices et quelques conjectures, Dissertation, Université du Québec à Montréal, 1992.

Simon Plouffe, 1031 Generating Functions, Appendix to Thesis, Montreal, 1992

Yash Puri and Thomas Ward, A dynamical property unique to the Lucas sequence, Fibonacci Quarterly, Volume 39, Number 5 (November 2001), pp. 398-402.

Yash Puri and Thomas Ward, Arithmetic and growth of periodic orbits, J. Integer Seqs., Vol. 4 (2001), #01.2.1.

José L. Ramírez, Gustavo N. Rubiano, and Rodrigo de Castro, A Generalization of the Fibonacci Word Fractal and the Fibonacci Snowflake, arXiv preprint arXiv:1212.1368 [cs.DM], 2012.

José L. Ramírez and Gustavo N. Rubiano, Properties and Generalizations of the Fibonacci Word Fractal, The Mathematica Journal, Vol. 16 (2014).

Mark A. Shattuck and Carl G. Wagner, Periodicity and Parity Theorems for a Statistic on r-Mino Arrangements, Journal of Integer Sequences, Vol. 9 (2006), Article 06.3.6.

N. J. A. Sloane, Illustration of initial terms: the Lucas tree

Zdzisław Skupień, Sums of Powered Characteristic Roots Count Distance-Independent Circular Sets, Discussiones Mathematicae Graph Theory. Volume 33, Issue 1, Pages 217-229, ISSN (Print) 2083-5892, DOI: 10.7151/dmgt.1658, April 2013.

Eric Weisstein's World of Mathematics, Lucas Number

Eric Weisstein's World of Mathematics, Lucas n-Step Number

Richard J. Yanco, Letter and Email to N. J. A. Sloane, 1994

Index entries for "core" sequences

Index entries for linear recurrences with constant coefficients, signature (1,1).

Index entries for sequences related to Benford's law

Expansion of x(1 + 2x)/(1 - x - x^2). - Simon Plouffe, dissertation 1992; multiplied by x. - R. J. Mathar, Nov 14 2007

a(n) = A000045(2n)/A000045(n). - Benoit Cloitre, Jan 05 2003

For n > 1, L(n) = F(n + 2) - F(n - 2), where F(n) is the n-th Fibonacci number (A000045). - Gerald McGarvey, Jul 10 2004

a(n+1) = 4*A054886(n+3) - A022388(n) - 2*A022120(n+1) (a conjecture; note that the above sequences have different offsets). Generating floretion: - 0.25'i - 0.5'k - 0.25i' - 0.5j' - 0.5k' - 0.75'ii' + 0.75'jj' + 0.25'kk' + 0.25'jk' - 0.5'ki' + 0.25'kj' - 0.25e. - Creighton Dement, Nov 27 2004

L(n) = (1/(n-1)!) * [ n^(n-1) - { -C(n-2, 0) + 2*C(n-2, 1) + 3*C(n-2, 2) }*n^(n-2) + { 2*C(n-3, 0) + 15*C(n-3, 1) + 51*C(n-3, 2) + 65*C(n-3, 3) + 27*C(n-3, 4) }*n^(n-3) - { -6*C(n-4, 0) + 148*C(n-4, 1) + 945*C(n-4, 2) + 2292*C(n-4, 3) + 2776*C(n-4, 4) + 1680*C(n-4, 5) + 405*C(n-4, 6) }*n^(n-4) + ... ]. - André F. Labossière, Nov 30 2004

a(n) = sum{k = 0..floor((n+1)/2), (n+1)*binomial(n - k + 1, k)/(n - k + 1)}. - Paul Barry, Jan 30 2005

L(n) = A000045(n+3) - 2*A000045(n). - Creighton Dement, Oct 07 2005

L(n) = (1/sqrt(5))*(2.5 + 0.5*sqrt(5))*(0.5 + 0.5*sqrt(5))^n + (1/sqrt(5))*(-2.5 + 0.5*sqrt(5))*(0.5 - 0.5*sqrt(5))^n. - Antonio Alberto Olivares, Feb 28 2006

L(n) = A000045(n+1) + A000045(n-1). - John Blythe Dobson, Sep 29 2007

a(n) = 2*fibonacci(n-1) + fibonacci(n), n >= 1. - Zerinvary Lajos, Oct 05 2007

L(n) is the term (1, 1) in the 1 x 2 matrix [2, -1].[1, 1; 1, 0]^n. - Alois P. Heinz, Jul 25 2008

a(n) = phi^n + (1 - phi)^n = phi^n + (-phi)^(-n) = ((1 + sqrt(5))^n + (1 - sqrt(5))^n)/(2^n) where phi is the golden ratio (A001622). - Artur Jasinski, Oct 05 2008

a(n) = A014217(n+1) - A014217(n-1). See A153263. - Paul Curtz, Dec 22 2008

a(n) = ((1 + sqrt5)^n - (1 - sqrt5)^n)/(2^n*sqrt5) + ((1 + sqrt5)^(n - 1) - (1 - sqrt5)^(n - 1))/(2^(n - 2)*sqrt5). - Al Hakanson (hawkuu(AT)gmail.com), Jan 12 2009, Jan 14 2009

From Hieronymus Fischer, Oct 20 2010 (Start)

Continued fraction for n odd: [L(n); L(n), L(n), ...] = L(n) + fract(Fib(n) * phi).

Continued fraction for n even: [L(n); -L(n), L(n), -L(n), L(n), ...] = L(n) - 1 + fract(Fib(n)*phi). Also: [L(n) - 2; 1, L(n) - 2, 1, L(n) - 2, ...] = L(n) - 2 + fract(Fib(n)*phi). (End)

INVERT transform of (1, 2, -1, -2, 1, 2, ...). - Gary W. Adamson, Mar 07 2012

L(2n - 1) = floor(phi^(2n - 1)); L(2n) = ceiling(phi^(2n)). - Thomas Ordowski, Jun 15 2012

a(n) = hypergeom([(1 - n)/2, -n/2], [1 - n], -4) for n >= 3. - Peter Luschny, Sep 03 2019

G.f. = x + 3*x^2 + 4*x^3 + 7*x^4 + 11*x^5 + 18*x^6 + 29*x^7 + 47*x^8 + ...

A000204 := proc(n) option remember; if n <=2 then 2*n-1; else procname(n-1)+procname(n-2); fi; end;

with(combinat): A000204 := n->fibonacci(n+1)+fibonacci(n-1);

# alternative Maple program:

L:= n-> (<<1|1>, <1|0>>^n. <<2, -1>>)[1, 1]:

seq(L(n), n=1..50);  # Alois P. Heinz, Jul 25 2008

# Alternative:

a := n -> `if`(n=1, 1, `if`(n=2, 3, hypergeom([(1-n)/2, -n/2], [1-n], -4))):

seq(simplify(a(n)), n=1..39); # Peter Luschny, Sep 03 2019

c = (1 + Sqrt[5])/2; Table[Expand[c^n + (1 - c)^n], {n, 30}] (* Artur Jasinski, Oct 05 2008 *)

Table[LucasL[n, 1], {n, 36}] (* Zerinvary Lajos, Jul 09 2009 *)

LinearRecurrence[{1, 1}, {1, 3}, 50] (* Sture Sjöstedt, Nov 28 2011 *)

lukeNum[n_] := If[n < 1, 0, LucasL[n]]; (* Michael Somos, May 18 2015 *)

lukeNum[n_] := SeriesCoefficient[x D[Log[1 / (1 - x - x^2)], x], {x, 0, n}]; (* Michael Somos, May 18 2015 *)

(PARI) A000204(n)=fibonacci(n+1)+fibonacci(n-1) \\ Michael B. Porter, Nov 05 2009

(Haskell)

a000204 n = a000204_list !! n

a000204_list = 1 : 3 : zipWith (+) a000204_list (tail a000204_list)

-- Reinhard Zumkeller, Dec 18 2011

(Sage)

def A000204():

    x, y = 1, 2

    while true:

       yield x

       x, y = x + y, x

a = A000204(); print([next(a) for i in range(39)])  # Peter Luschny, Dec 17 2015

(MAGMA) [Lucas(n): n in [1..30]]; // G. C. Greubel, Dec 17 2017

(Scala) def lucas(n: BigInt): BigInt = {

  val zero = BigInt(0)

  def fibTail(n: BigInt, a: BigInt, b: BigInt): BigInt = n match {

    case `zero` => a

    case _ => fibTail(n - 1, b, a + b)

  }

  fibTail(n, 2, 1)

}

(1 to 50).map(lucas(_)) // Alonso del Arte, Oct 20 2019

Cf. A000032, A000045, A061084, A027960, A001609, A014097, A000079, A003269, A003520, A005708, A005709, A005710, A006206, A101033, A101032, A100492, A099731, A094216, A094638, A000108, A090946 (complement).

Sequence in context: A100581 A093090 A193686 * A075193 A042433 A024319

Adjacent sequences:  A000201 A000202 A000203 * A000205 A000206 A000207

core,easy,nonn,nice

N. J. A. Sloane

Additional comments from Yong Kong (ykong(AT)curagen.com), Dec 16 2000

Plouffe Maple line edited by N. J. A. Sloane, May 13 2008

approved