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%I #8 Aug 20 2021 13:18:09
%S 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,
%T 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,
%U 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
%N a(n) = 1 if sigma(n)-1 is a prime, 0 otherwise.
%C Characteristic function of A248792, numbers n such that sigma(n) - 1 is a prime.
%H Antti Karttunen, <a href="/A296211/b296211.txt">Table of n, a(n) for n = 1..65537</a>
%H <a href="/index/Ch#char_fns">Index entries for characteristic functions</a>
%F a(1) = 0; for n > 1, a(n) = A010051(A000203(n)-1) = A010051(A039653(n)).
%F a(n) >= A010051(n).
%t Table[If[PrimeQ[DivisorSigma[1,n]-1],1,0],{n,120}] (* _Harvey P. Dale_, Aug 20 2021 *)
%o (Scheme) (define (A296211 n) (if (= 1 n) 0 (A010051 (+ -1 (A000203 n)))))
%Y Cf. A000203, A010051, A039653, A248792 (positions of ones), A296091, A296212.
%K nonn
%O 1
%A _Antti Karttunen_, Dec 07 2017
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