This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A236373 #16 Jun 05 2014 23:18:34 %S A236373 2047,8388607,140737488355327,576460752303423487 %N A236373 Pseudoprimes to base 2 of the form 6p+1 such that 2^(p-1) == 1 (mod p). %C A236373 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 A236373 Composite 2^n-1 belong to this sequence when n is in A005385 (e.g., 2^83-1, 2^167-1, etc.) %C A236373 No other terms below 2^64. - _Max Alekseyev_, May 28 2014 %e A236373 2047=6*341+1; 2^2046 == 1 (mod 2047); 2^340 == 1 (mod 341). %Y A236373 Subsequence of A001567. %K A236373 nonn,more %O A236373 1,1 %A A236373 _Alzhekeyev Ascar M_, Jan 24 2014 %E A236373 a(4) from _Max Alekseyev_, May 28 2014