A274511 a(n) is the only number m such that 7^(2^m) + 1 is divisible by A273948(n).

1, 3, 7, 4, 7, 2, 10, 9, 6, 15, 11, 14, 3, 5, 11, 12, 8, 17, 19, 5, 7, 21, 21, 4, 34, 25, 5, 9, 6, 20, 32, 17, 31, 40

Offset: 1

Author

Arkadiusz Wesolowski, Jun 25 2016

Keywords

• nonn
• more

Crossrefs

Cf. A273948.

Programs

Mathematica

t = Select[Prime@ Range[3, 10^7], IntegerQ@ Log2@ MultiplicativeOrder[7, #] &]; Table[SelectFirst[Range@ 100, Divisible[7^(2^#) + 1, t[[n]]] &], {n, Length@ t}] (* Michael De Vlieger, Jun 29 2016, after Arkadiusz Wesolowski at A273948 *)

PARI

forstep(p=3, 10^15, 2, if(!Mod(p, 7)==0, if(isprime(p), o=znorder(Mod(7, p)); x=ispower(2*o); if(2^(x-1)==o, print1(x-2, ", ")))));