This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A125570 #18 Dec 29 2023 11:53:42
%S A125570 3,7,8,19,69,77,104,107,162,163,399,4787,4818
%N A125570 Numbers n such that Sum_(x=1..n) (x-1)*6^(x-1)/6 is prime.
%C A125570 No more terms through 10^4.
%C A125570 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 A125570 s = 0; Do[s += (x-1)*6^(x-1)/6; If[PrimeQ[s], Print[x]], {x, 10^4}]
%Y A125570 Cf. A119529.
%K A125570 hard,more,nonn
%O A125570 1,1
%A A125570 _Ryan Propper_, Jan 01 2007