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 A138843 #4 Dec 28 2012 11:18:31 %S A138843 66,28,46,88,36,86,18,28,26,16,18,18,26,18,58,18,96,36,16,48,16,56,36, %T A138843 96,16,86,36,18,18,16,28,18,86,88,36,16,86,96,46 %N A138843 Concatenation of initial and final digits of n-th perfect number. %C A138843 Also, concatenation of A135617(n) and A094540(n). %e A138843 a(5)=36 because the 5th perfect number A000396(5) is 33550336 and the concatenation of initial and final digits of 33550336 is 36. %Y A138843 Cf. A000396, A073729, A135617, A094540, A138840, A138841, A138842, A138844. %K A138843 base,nonn,less %O A138843 1,1 %A A138843 _Omar E. Pol_, Apr 02 2008