A081334 a(n) = sigma(2*n^2) modulo 4.

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

Offset

1,1

Links

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

Formula

a(n) = A010873(A065765(n)). - Amiram Eldar, May 03 2025

Mathematica

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

Prog

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

Crossrefs

Cf. A000203, A010873, A065765, A081325.

Sequence in context: A358691 A172368 A138070 * A106694 A183051 A031355

Adjacent sequences: A081331 A081332 A081333 * A081335 A081336 A081337

Keyword

nonn,easy

Author

Benoit Cloitre, Apr 20 2003

Status

approved