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 A274512 #10 Oct 25 2019 12:28:12 %S A274512 0,3,2,1,2,7,4,4,4,4,8,7,5,15,4,7,5,9,15,3,5,8,16,19,20,17,9,12,18,6, %T A274512 26,8,29,8,11,19,29,35,19,40,22,41,40,5 %N A274512 a(n) is the only number m such that 10^(2^m) + 1 is divisible by A072982(n+1). %F A274512 a(n) = A197224(n+1) - 1. - _Ray Chandler_, Oct 25 2019 %o A274512 (PARI) forstep(p=3, 10^15, 2, if(!Mod(p, 5)==0, if(isprime(p), o=znorder(Mod(10, p)); x=ispower(2*o); if(2^(x-1)==o, print1(x-2, ", "))))); %Y A274512 Cf. A072982, A197224. %K A274512 nonn,more %O A274512 1,2 %A A274512 _Arkadiusz Wesolowski_, Jun 25 2016