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 A375793 #25 Sep 23 2024 11:33:20 %S A375793 1,3,5,11,13,29,37,61,73,131,157,181,193,277,313,397,421,457,541,561, %T A375793 613,661,673,733,757,877,997,1093,1153,1201,1213,1237,1289,1321,1381, %U A375793 1453,1621,1657,1753,1873,1905,1933,1993,2017,2137,2341,2473,2557,2593,2797,2857,2917,3061,3217,3253,3313,3389,3457 %N A375793 Numbers m such that 2^m == 2 (mod m-th triangular number). %C A375793 a(19) = 561 is the first composite term of the sequence. %H A375793 Alois P. Heinz, <a href="/A375793/b375793.txt">Table of n, a(n) for n = 1..10000</a> %p A375793 t:= n-> n*(n+1)/2: %p A375793 q:= m-> is(2&^m-2 mod t(m)=0): %p A375793 select(q, [$1..3457])[]; # _Alois P. Heinz_, Sep 21 2024 %t A375793 Select[Range[3457],Mod[2^#-2,#(#+1)/2 ]==0&] (* _James C. McMahon_, Sep 23 2024 *) %o A375793 (Magma) [1] cat [m: m in [2..3500] | Modexp(2, m, m*(m+1) div 2) eq 2]; %Y A375793 Supersequence of A216822, A217465, A217466 and A375792. %Y A375793 Cf. A000217, A272934, A289382. %K A375793 nonn %O A375793 1,2 %A A375793 _Juri-Stepan Gerasimov_, Aug 29 2024