A296211 - OEIS

A296211

a(n) = 1 if sigma(n)-1 is a prime, 0 otherwise.

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

(list; graph; refs; listen; history; text; internal format)

OFFSET

COMMENTS

Characteristic function of A248792, numbers n such that sigma(n) - 1 is a prime.

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..65537

Index entries for characteristic functions

FORMULA

a(1) = 0; for n > 1, a(n) = A010051(A000203(n)-1) = A010051(A039653(n)).

a(n) >= A010051(n).

MATHEMATICA

Table[If[PrimeQ[DivisorSigma[1, n]-1], 1, 0], {n, 120}] (* Harvey P. Dale, Aug 20 2021 *)