A179211 - OEIS

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A179211

Number of squarefree numbers between n and 2*n (inclusive).

2, 2, 3, 3, 4, 4, 5, 5, 6, 7, 8, 8, 9, 8, 9, 9, 11, 11, 13, 13, 15, 15, 15, 15, 15, 16, 16, 17, 19, 19, 20, 19, 21, 21, 22, 22, 24, 23, 24, 24, 25, 25, 26, 26, 27, 28, 29, 29, 30, 30, 32, 32, 34, 34, 36, 36, 38, 38, 38, 38, 39, 39, 38, 39, 41, 41, 42, 41, 43, 43, 44, 44, 46, 45, 45 (list; graph; refs; listen; history; text; internal format)

	OFFSET	`1,1`
	COMMENTS	`a(n) > A035250(n) for n>2;` `A179212(n) = a(n+1) - a(n);` `a(n) = A013928(2*n+1) - A013928(n).`
	LINKS	`Charles R Greathouse IV, Table of n, a(n) for n = 1..10000`
	FORMULA	`a(n) = SUM(A008966(k): n <= k <= 2*n).`
	MAPLE	`a := n -> nops(select(issqrfree, [$n..(2*n)])):` `seq(a(n), n=1..75); # Peter Luschny, Mar 02 2017`
	PROG	`(PARI) f(n)=my(s); forfactored(k=1, sqrtint(n), s += n\k[1]^2moebius(k)); s` `a(n)=f(2n)-f(n-1) \\ Charles R Greathouse IV, Nov 05 2017`
	CROSSREFS	`Cf. A179213, A179214, A061398, A005117.` `Sequence in context: A194245 A284007 A261133 * A180639 A025766 A025158` `Adjacent sequences: A179208 A179209 A179210 * A179212 A179213 A179214`
	KEYWORD	`nonn`
	AUTHOR	`Reinhard Zumkeller, Jul 05 2010`
	STATUS	`approved`

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Last modified January 10 06:07 EST 2018. Contains 297376 sequences.