A374474 - OEIS

A374474

a(n) = 1 if the least prime dividing the sum of divisors of n is equal to the least prime not dividing n, otherwise a(n) = 0.

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

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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) = [A020639(A000203(n)) = A053669(n)], where [ ] is the Iverson bracket.

PROG

(PARI)

A020639(n) = if(1==n, n, vecmin(factor(n)[, 1]));

A053669(n) = forprime(p=2, , if(n%p, return(p)));

A374474(n) = (A020639(sigma(n))==A053669(n));