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 A139233 #14 Oct 20 2023 08:39:14 %S A139233 223,3582,16767288,4261388256,60146251776,1152921370926219264, %T A139233 1329227995784915870021503368556314624, %U A139233 95780971304118050988940697472320075563727548890218496 %N A139233 Second differences of perfect numbers A000396, divided by 2. %H A139233 Paolo Xausa, <a href="/A139233/b139233.txt">Table of n, a(n) for n = 1..13</a> %F A139233 a(n) = A139230(n)/2. %t A139233 Differences[PerfectNumber[Range[12]],2]/2 (* _Paolo Xausa_, Oct 20 2023 *) %Y A139233 Cf. A000396, A139228, A139229, A139230, A139231, A139232, A139234, A139235, A139236, A139237. %K A139233 nonn %O A139233 1,1 %A A139233 _Omar E. Pol_, Apr 19 2008 %E A139233 a(5)-a(8) from _Jinyuan Wang_, Mar 04 2020