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 A139293 #9 Jun 22 2022 01:56:12 %S A139293 0,3,63,1023,262143,4194303,1073741823,17179869183,4398046511103, %T A139293 18014398509481983,288230376151711743,1180591620717411303423, %U A139293 302231454903657293676543,4835703278458516698824703 %N A139293 (2^(2p - 1)/8)-1, where p is prime. %F A139293 a(n) = (A139286(n)/8)-1. %t A139293 (2^(2#-1))/8-1&/@Prime[Range[30]] (* _Harvey P. Dale_, May 09 2012 *) %Y A139293 Cf. A139286, A139287, A139288, A139289, A139290, A139291, A139292, A139294, A139306. %K A139293 nonn %O A139293 1,2 %A A139293 _Omar E. Pol_, Apr 13 2008 %E A139293 More terms from _Jon E. Schoenfield_, Jul 16 2010