A081325 a(n) = sigma(n^2) modulo 4.

1, 3, 1, 3, 3, 3, 1, 3, 1, 1, 1, 3, 3, 3, 3, 3, 3, 3, 1, 1, 1, 3, 1, 3, 1, 1, 1, 3, 3, 1, 1, 3, 1, 1, 3, 3, 3, 3, 3, 1, 3, 3, 1, 3, 3, 3, 1, 3, 1, 3, 3, 1, 3, 3, 3, 3, 1, 1, 1, 1, 3, 3, 1, 3, 1, 3, 1, 1, 1, 1, 1, 3, 3, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 3, 1, 3, 3, 3, 3, 1, 3, 3, 1, 3, 3, 3, 3, 3, 1, 3, 3, 1, 1, 1, 3

Offset: 1

Author

Benoit Cloitre, Apr 20 2003

Keywords

• nonn
• easy

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000203, A010873, A065764, A081334, A081339, A081354.

Programs

Mathematica

a[n_] := Mod[DivisorSigma[1, n^2], 4]; Array[a, 100] (* Amiram Eldar, May 03 2025 *)

PARI

a(n) = sigma(n^2) % 4; \\ Amiram Eldar, May 03 2025

Formula

From Amiram Eldar, May 03 2025: (Start)

a(n) = A010873(A065764(n)).

a(A081339(n)) = 1.

a(A081354(n)) = 3. (End)