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A296211
a(n) = 1 if sigma(n)-1 is a prime, 0 otherwise.
3
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.
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: A030190 A353471 A157658 * A341642 A123506 A051105
KEYWORD
nonn
AUTHOR
Antti Karttunen, Dec 07 2017
STATUS
approved