A339965 a(n) = sigma(n) / gcd(sigma(n),n+1).

1, 1, 1, 7, 1, 12, 1, 5, 13, 18, 1, 28, 1, 8, 3, 31, 1, 39, 1, 2, 16, 36, 1, 12, 31, 14, 10, 56, 1, 72, 1, 21, 24, 54, 4, 91, 1, 20, 7, 90, 1, 96, 1, 28, 39, 72, 1, 124, 57, 31, 18, 98, 1, 24, 9, 40, 40, 90, 1, 168, 1, 32, 13, 127, 14, 144, 1, 42, 48, 144, 1, 195, 1, 38, 31, 20, 16, 168, 1, 62, 121, 126, 1, 224, 54, 44

Offset: 1

Author

Antti Karttunen, Dec 25 2020

Keywords

• nonn
• frac
• easy

Links

• Antti Karttunen, Table of n, a(n) for n = 1..10080
• Antti Karttunen, Data supplement: n, a(n) computed for n = 1..65537
• Index entries for sequences related to sigma(n)

Crossrefs

Cf. A000203, A339964, A339966 (denominators).

Cf. A017665.

Cf. also A160595.

Programs

Mathematica

Table[DivisorSigma[1, n]/GCD[DivisorSigma[1, n], n + 1], {n, 80}] (* Wesley Ivan Hurt, Oct 10 2021 *)

PARI

A339965(n) = sigma(n)/(gcd(sigma(n),n+1));

Formula

a(n) = A000203(n) / A339964(n).

a(n) = numerator(sigma(n)/(n+1)). - Michel Marcus, Jan 07 2023