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 A138817 #5 Mar 11 2014 01:34:11 %S A138817 326,748,166,748,166,166,748,748,166,166,748,748,166,748,748,748,166, %T A138817 166,166,748,166,166,166,166,166,166,166,748,748,166,748,748,166,748, %U A138817 166,166,166,166,166 %N A138817 Concatenation of final digit of n-th Mersenne prime A000668(n), final digit of n-th even superperfect number A061652(n) and final digit of n-th perfect number A000396(n). %C A138817 Also, concatenation of final digit of n-th Mersenne prime A000668(n), final digit of n-th superperfect number A019279(n) and final digit of n-th perfect number A000396(n), if there are no odd superperfect numbers. %C A138817 Also, concatenation of n-th term of A080172, A138125(n) and A094540(n). %C A138817 a(1)=326. For n>1 a(n) is equal to 166 or 748, only. %H A138817 L. C. Noll, <a href="http://www.isthe.com/chongo/tech/math/prime/mersenne.html">Mersenne Prime Digits and Names</a>. %H A138817 Omar E. Pol, <a href="http://www.polprimos.com">Determinacion geometrica de los numeros primos y perfectos</a>. %Y A138817 Cf. A000396, A000668, A019279, A061652, A080172, A094540, A138125, A138817. %K A138817 base,nonn,less %O A138817 1,1 %A A138817 _Omar E. Pol_, Apr 01 2008