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 A274511 a(n) is the only number m such that 7^(2^m) + 1 is divisible by A273948(n). 0

%I

%S 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,

%T 6,20,32,17,31,40

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

%t 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 *)

%o (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, ", ")))));

%Y Cf. A273948.

%K nonn,more

%O 1,2

%A _Arkadiusz Wesolowski_, Jun 25 2016

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Last modified December 7 03:00 EST 2019. Contains 329836 sequences. (Running on oeis4.)