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A354160
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Products of exactly two distinct primes in A090252, in order of appearance.
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4
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21, 55, 26, 85, 57, 161, 319, 217, 481, 205, 731, 517, 159, 1121, 1403, 871, 355, 1241, 869, 2407, 1691, 413, 3007, 2323, 206, 1391, 4033, 565, 5207, 2227, 5891, 6533, 4321, 453, 1007, 623, 4867, 2231, 6161, 2119, 11189, 6401, 12709, 7421, 2159, 9563, 8213, 1507, 15247, 9259, 4031, 12367, 597, 2869, 11183, 1561, 13393, 7099, 3611, 14213, 478, 24823
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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LINKS
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Michael De Vlieger, Table of n, a(n) for n = 1..2517
Michael De Vlieger, Annotated log-log scatterplot of A090252(n), n = 1..2^12, labeling primes in red, highlighting composite prime powers in gold, squarefree semiprimes in green and labeling them in boldface.
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MATHEMATICA
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Select[Import["https://oeis.org/A090252/b090252.txt", "Data"][[1 ;; 2000, -1]], PrimeNu[#] == PrimeOmega[#] == 2 &] (* Michael De Vlieger, Jun 16 2022 *)
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PROG
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(Python)
from itertools import count, islice
from collections import deque
from math import gcd, lcm
from sympy import factorint
def A354160_gen(): # generator of terms
aset, aqueue, c, b, f = {1}, deque([1]), 2, 1, True
while True:
for m in count(c):
if m not in aset and gcd(m, b) == 1:
if len(fm := factorint(m)) == sum(fm.values()) == 2:
yield m
aset.add(m)
aqueue.append(m)
if f: aqueue.popleft()
b = lcm(*aqueue)
f = not f
while c in aset:
c += 1
break
A354160_list = list(islice(A354160_gen(), 25)) # Chai Wah Wu, May 31 2022
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CROSSREFS
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Cf. A090252, A354159, A354161, A354162, A354163.
Sequence in context: A304517 A007796 A211460 * A190664 A144302 A347373
Adjacent sequences: A354157 A354158 A354159 * A354161 A354162 A354163
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane, May 30 2022
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STATUS
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approved
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