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 A138820 #2 Mar 30 2012 17:33:54 %S A138820 236,4728,1631496,641278128,4096819133550336,655361310718589869056, %T A138820 262144524287137438691328,107374182421474836472305843008139952128, %U A138820 115292150460684697623058430092136939512658455991569831744654692615953842176 %N A138820 Concatenation of n-th even superperfect number, n-th Mersenne prime A000668(n) and n-th perfect number. %C A138820 Concatenation of A061652(n), A000668(n) and A000396(n). %C A138820 Also concatenation of n-th superperfect number, n-th Mersenne prime A000668(n) and n-th perfect number, if there are no odd superperfect numbers. %Y A138820 Cf. A000396, A000668, A019279, A061652, A138818, A138819. %K A138820 base,nonn %O A138820 1,1 %A A138820 _Omar E. Pol_, Apr 05 2008