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%I #10 Jan 30 2020 04:49:16
%S 1,2,3,4,5,7,8,12,19,35,39,44,56,65,77,95,104,144,207,217,307,325,392,
%T 459,471,828,1275,3277,4205,5135,7560,12677,14899,18124,18820,25691,
%U 26460,41629,51388,71784,80331,85688,88172,97064,123631,155931,164988,234761,414841
%N Numbers n such that 3*2^(n-1) - 1 is prime.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/ThabitibnKurrahRule.html">Thabit ibn Kurrah's rules</a>
%F a(n) = A002235(n) + 1. - _Jinyuan Wang_, Jan 30 2020
%e 3*2^(3-1) - 1 = 11 so a(1) = 3.
%t Do[If[PrimeQ[3*2^(n - 1) - 1], Print[n]], {n, 1, 8000}] (* Mohammed Bouayoun (Mohammed.Bouayoun(AT)yahoo.fr), Apr 13 2006 *)
%o (PARI) for (i=1,1000,if(isprime(3*2^(i-1)-1),print1(i,",")))
%Y Cf. A002235.
%K nonn
%O 1,2
%A Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Mar 17 2004
%E More terms from Mohammed Bouayoun (Mohammed.Bouayoun(AT)yahoo.fr), Apr 13 2006
%E More terms from _Jinyuan Wang_, Jan 30 2020
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