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 A134709 #5 Mar 14 2020 05:55:37 %S A134709 0,1,7,31,2047,32767,131071,536870911,576460752303423487, %T A134709 154742504910672534362390527,40564819207303340847894502572031, %U A134709 42535295865117307932921825928971026431 %N A134709 Even superperfect numbers divided by 2, minus 1. %F A134709 a(n) = (A061652(n)/2) - 1. %e A134709 a(5)=2047 because the 5th even superperfect number is 4096 and (4096/2)-1=2047. %Y A134709 Cf. A019279, A061652, A133028. %K A134709 nonn %O A134709 1,3 %A A134709 _Omar E. Pol_, Nov 07 2007 %E A134709 More terms from _Jinyuan Wang_, Mar 14 2020