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

Offset

1

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 *)

Prog

(Scheme) (define (A296211 n) (if (= 1 n) 0 (A010051 (+ -1 (A000203 n)))))

Crossrefs

Cf. A000203, A010051, A039653, A248792 (positions of ones), A296091, A296212.

Sequence in context: A377870 A353471 A157658 * A341642 A123506 A051105

Adjacent sequences: A296208 A296209 A296210 * A296212 A296213 A296214

Keyword

nonn

Author

Antti Karttunen, Dec 07 2017

Status

approved