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%I #18 Dec 29 2023 11:53:42
%S 3,7,8,19,69,77,104,107,162,163,399,4787,4818
%N Numbers n such that Sum_(x=1..n) (x-1)*6^(x-1)/6 is prime.
%C No more terms through 10^4.
%C Note that Sum(x=1,n,(x-1)*6^(x-1))/6 = (6^(n-1)*(5*n-6)+1)/25. Therefore this sequence consists of n such that (6^(n-1)*(5*n-6)+1)/25 is prime. - _Max Alekseyev_, Oct 18 2008
%t s = 0; Do[s += (x-1)*6^(x-1)/6; If[PrimeQ[s], Print[x]], {x, 10^4}]
%Y Cf. A119529.
%K hard,more,nonn
%O 1,1
%A _Ryan Propper_, Jan 01 2007
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