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 A139568 #5 Mar 14 2020 09:20:35 %S A139568 32,8192,8589934592,2305843009213693952, %T A139568 191561942608236107294793378393788647952342390272950272 %N A139568 Bisection of ultraperfect numbers A139306. %H A139568 Jinyuan Wang, <a href="/A139568/b139568.txt">Table of n, a(n) for n = 1..7</a> %F A139568 a(n) = A139306(2*n). - _Jinyuan Wang_, Mar 14 2020 %Y A139568 Cf. A099057, A099058, A139306, A139563, A139564, A139567. %K A139568 nonn %O A139568 1,1 %A A139568 _Omar E. Pol_, May 08 2008