A186428 a(n) = sigma(n^2) modulo sigma(n).

0, 1, 1, 3, 1, 7, 1, 7, 4, 1, 1, 11, 1, 15, 19, 15, 1, 28, 1, 37, 5, 31, 1, 31, 6, 21, 13, 31, 1, 13, 1, 31, 1, 43, 39, 20, 1, 27, 27, 67, 1, 3, 1, 7, 7, 55, 1, 71, 8, 73, 31, 87, 1, 91, 19, 39, 73, 67, 1, 61, 1, 39, 33, 63, 45, 7, 1, 67, 85, 129, 1, 157, 1, 45, 109, 51, 93, 21, 1, 31, 40, 91, 1, 123, 13, 51, 43, 151, 1, 49, 15, 7, 109, 103, 51, 151, 1, 113, 25, 124, 1, 73, 1, 141, 123, 115, 1, 3, 1, 133, 51, 111, 1, 111, 7, 121, 121

Offset

1,4

Comments

a(n)=1 iff n is prime. Apparently a(n)>2 for composite n's.

Links

Antti Karttunen, Table of n, a(n) for n = 1..20000

Index entries for sequences related to sigma(n).

Formula

a(n) = A065764(n) mod A000203(n).

Mathematica

Table[Mod[DivisorSigma[1, n^2], DivisorSigma[1, n]], {n, 200000}]

Prog

(PARI) A186428(n) = (sigma(n^2)%sigma(n)); \\ Antti Karttunen, Jan 22 2025

Crossrefs

Cf. A000203, A065764.

Sequence in context: A316553 A347959 A347963 * A323599 A167515 A140435

Adjacent sequences: A186425 A186426 A186427 * A186429 A186430 A186431

Keyword

nonn,easy

Author

Zak Seidov, Mar 06 2011

Status

approved