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 A347886 Odd numbers k such that sigma(k^2) has an even number of prime factors when counted with multiplicity. 2
 1, 7, 9, 11, 13, 15, 19, 23, 25, 29, 31, 43, 47, 51, 53, 63, 67, 73, 77, 79, 81, 83, 85, 91, 97, 99, 103, 105, 111, 113, 117, 121, 123, 127, 133, 135, 143, 147, 157, 161, 163, 165, 171, 175, 177, 179, 183, 185, 191, 195, 197, 199, 203, 205, 207, 209, 211, 213, 217, 223, 225, 227, 233, 239, 241, 243, 245, 247, 251, 253 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Equally, odd numbers k such that A003415(sigma(k^2)) is even, i.e., k^2 is in A347878. See A235991. LINKS Table of n, a(n) for n=1..70. Index entries for sequences related to sigma(n) MATHEMATICA Select[Range[1, 250, 2], EvenQ[PrimeOmega[DivisorSigma[1, #^2]]] &] (* Amiram Eldar, Sep 19 2021 *) PROG (PARI) isA347886(n) = ((n%2)&&!(bigomega(sigma(n^2))%2)); CROSSREFS Cf. A000203, A001222, A003415, A005820, A235991, A342923, A342925, A347391, A347870, A347878, A347882, A347885 (complement among A005408). Sequence in context: A020742 A193071 A329112 * A023389 A248963 A221636 Adjacent sequences: A347883 A347884 A347885 * A347887 A347888 A347889 KEYWORD nonn AUTHOR Antti Karttunen, Sep 19 2021 STATUS approved

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Last modified July 23 23:47 EDT 2024. Contains 374575 sequences. (Running on oeis4.)