A236373 - OEIS

%I #16 Jun 05 2014 23:18:34

%S 2047,8388607,140737488355327,576460752303423487

%N Pseudoprimes to base 2 of the form 6p+1 such that 2^(p-1) == 1 (mod p).

%C The first four terms are A065341(1), A065341(2), A065341(7), A065341(9) and have the form 2^m-1. Are there terms not of this form?

%C Composite 2^n-1 belong to this sequence when n is in A005385 (e.g., 2^83-1, 2^167-1, etc.)

%C No other terms below 2^64. - _Max Alekseyev_, May 28 2014

%e 2047=6*341+1; 2^2046 == 1 (mod 2047); 2^340 == 1 (mod 341).

%Y Subsequence of A001567.

%K nonn,more

%O 1,1

%A _Alzhekeyev Ascar M_, Jan 24 2014

%E a(4) from _Max Alekseyev_, May 28 2014