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 A139289 #10 Aug 13 2025 10:19:03
%S A139289 3,15,255,4095,1048575,16777215,4294967295,68719476735,17592186044415,
%T A139289 72057594037927935,1152921504606846975,4722366482869645213695,
%U A139289 1208925819614629174706175,19342813113834066795298815,4951760157141521099596496895,20282409603651670423947251286015,83076749736557242056487941267521535
%N A139289 (2^(2p - 1)/2)-1, where p is prime.
%H A139289 Floris P. van Doorn and Jasper Mulder, <a href="/A139289/b139289.txt">Table of n, a(n) for n=1..260</a>.
%F A139289 a(n) = A139286(n)/2 - 1.
%t A139289 Table[(2^(2 Prime[p] - 1)/2) - 1, {p, 1, 20}] (* _Floris P. van Doorn_ and Jasper Mulder (florisvandoorn(AT)hotmail.com), Oct 12 2009 *)
%Y A139289 Cf. A139286, A139287, A139288, A139290, A139291, A139292, A139293, A139294, A139306.
%K A139289 nonn
%O A139289 1,1
%A A139289 _Omar E. Pol_, Apr 13 2008
%E A139289 More terms from _Floris P. van Doorn_ and Jasper Mulder (florisvandoorn(AT)hotmail.com), Oct 12 2009