A389199 - OEIS

A389199

Numbers whose sum of squarefree divisors (A048250) is congruent to 2 modulo 4.

5, 10, 13, 17, 20, 25, 26, 29, 34, 37, 40, 41, 50, 52, 53, 58, 61, 68, 73, 74, 80, 82, 89, 97, 100, 101, 104, 106, 109, 113, 116, 122, 125, 136, 137, 146, 148, 149, 157, 160, 164, 169, 173, 178, 181, 193, 194, 197, 200, 202, 208, 212, 218, 226, 229, 232, 233, 241, 244, 250, 257, 269, 272, 274, 277, 281, 289, 292

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OFFSET

1,1

COMMENTS

Numbers k such that the odd part of k [= A000265(k)] is a prime power, p^e, e >= 1, and that prime p is of the form 4u+1.

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..10000

FORMULA

{k | A048250(k) == 2 (mod 4)}.

{k | A001221(A000265(k)) == 1 and A020639(A000265(k)) == 1 (mod 4)}.

MATHEMATICA

A389199Q[k_] := k > 1 && Mod[Times @@ (FactorInteger[k][[All, 1]] + 1), 4] == 2;