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%I #11 Apr 11 2022 12:57:09
%S 1,2,3,4,5,7,9,11,12,18,21,24,25,28,35,45,46,50,56,70,73,76,78,79,82,
%T 89,94,105,113,116,118,121,123,124,138,139,153,157,159,164,197,201,
%U 203,210,217,253,261,273,280,283,287,342,352,356,381,396,437,450,471
%N Numbers k such that A004394(k)+1 is prime.
%C First differs from A306587 at n=11.
%H Amiram Eldar, <a href="/A353301/b353301.txt">Table of n, a(n) for n = 1..300</a>
%e 1 is a term since A004394(1)+1 = 1+1 = 2 is prime.
%t s = {}; abm = 0; k = 0; Do[ab = DivisorSigma[-1, n]; If[ab > abm, abm = ab; k++; If[PrimeQ[n + 1], AppendTo[s, k]]], {n, 1, 10^6}]; s
%Y Cf. A004394, A072828, A306587, A353300, A353302.
%K nonn
%O 1,2
%A _Amiram Eldar_, Apr 10 2022
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