A353811 - OEIS

A353811

a(n) = 1 if sigma(n) is odd, and has an odd number of prime factors (with multiplicity), otherwise 0. Here sigma is the sum of divisors function.

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

Index entries for sequences related to sigma(n)

FORMULA

a(n) = A053866(n) * A353810(n).

a(n) = A353558(A000203(n)).

a(n) = A347870(n) - A353812(n).

MATHEMATICA

a[n_] := If[OddQ[s = DivisorSigma[1, n]] && OddQ[PrimeOmega[s]], 1, 0]; Array[a, 100] (* Amiram Eldar, May 13 2022 *)