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 A138816 #12 Jul 24 2024 04:52:29 %S A138816 326,742,314,168,843,168,521,212,212,631,181,181,632,521,155 %N A138816 Concatenation of initial digit of n-th Mersenne prime A000668(n), initial digit of n-th even superperfect number A061652(n) and initial digit of n-th perfect number A000396(n). %C A138816 Also, concatenation of initial digit of n-th Mersenne prime A000668(n), initial digit of n-th superperfect number A019279(n) and initial digit of n-th perfect number A000396(n), if there are no odd superperfect numbers. %C A138816 Also, concatenation of A135613(n), A138124(n) and A135617(n). %H A138816 L. C. Noll, <a href="http://www.isthe.com/chongo/tech/math/prime/mersenne.html">Mersenne Prime Digits and Names</a>. %H A138816 Omar E. Pol, <a href="http://www.polprimos.com">Determinacion geometrica de los numeros primos y perfectos</a>. %Y A138816 Cf. A000396, A000668, A019279, A061652, A135613, A135617, A138124, A138817. %K A138816 base,nonn,more %O A138816 1,1 %A A138816 _Omar E. Pol_, Apr 01 2008 %E A138816 a(13)-a(15) from _Robert Price_, Jun 16 2019