A355938 - OEIS

A355938

a(n) = 1 if sigma(n^2) is a noncomposite, otherwise 0.

1, 1, 1, 1, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1

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OFFSET

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..100000

Index entries for characteristic functions

FORMULA

a(n) = A080339(A000203(n^2)) = A080339(A065764(n)).

For all n >= 1, a(n) <= A010055(n).

MATHEMATICA

a[n_] := If[!CompositeQ[DivisorSigma[1, n^2]], 1, 0]; Array[a, 100] (* Amiram Eldar, Jul 21 2022 *)

PROG

(PARI) A355938(n) = ((1==n)||isprime(sigma(n^2)));