A347886 Odd numbers k such that sigma(k^2) has an even number of prime factors when counted with multiplicity.

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

Offset: 1

Author

Antti Karttunen, Sep 19 2021

Keywords

• nonn

Comments

Equally, odd numbers k such that A003415(sigma(k^2)) is even, i.e., k^2 is in A347878. See A235991.

Links

• Index entries for sequences related to sigma(n)

Crossrefs

Cf. A000203, A001222, A003415, A005820, A235991, A342923, A342925, A347391, A347870, A347878, A347882, A347885 (complement among A005408).

Programs

Mathematica

Select[Range[1, 250, 2], EvenQ[PrimeOmega[DivisorSigma[1, #^2]]] &] (* Amiram Eldar, Sep 19 2021 *)

PARI

isA347886(n) = ((n%2)&&!(bigomega(sigma(n^2))%2));