%I
%S 2047,8388607,140737488355327,576460752303423487
%N Pseudoprimes to base 2 of the form 6p+1 such that 2^(p1) == 1 (mod p).
%C The first four terms are A065341(1), A065341(2), A065341(7), A065341(9) and have the form 2^m1. Are there terms not of this form?
%C Composite 2^n1 belong to this sequence when n is in A005385 (e.g., 2^831, 2^1671, 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
