A274512 - OEIS

%I #10 Oct 25 2019 12:28:12

%S 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 26,8,29,8,11,19,29,35,19,40,22,41,40,5

%N a(n) is the only number m such that 10^(2^m) + 1 is divisible by A072982(n+1).

%F a(n) = A197224(n+1) - 1. - _Ray Chandler_, Oct 25 2019

%o (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 Cf. A072982, A197224.

%K nonn,more

%O 1,2

%A _Arkadiusz Wesolowski_, Jun 25 2016