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 A138839 #2 Mar 30 2012 17:33:54 %S A138839 33,14,23,44,18,43,9,14,13,8,9,9,13,9,29,9,48,18,8,24,8,28,18,48,8,43, %T A138839 18,9,9,8,14,9,43,44,18,8,43,48,23 %N A138839 Concatenation of initial and final digits of n-th perfect number, divided by 2. %C A138839 Also, concatenation of A135617(n) and A094540(n), divided by 2. %e A138839 a(5)=18 because the 5th perfect number A000396(5) is 33550336 and the concatenation of initial and final digits of 33550336 is 36 and 36/2 = 18. %Y A138839 Cf. A000396, A073729, A135617, A094540, A138843. %K A138839 base,easy,nonn %O A138839 1,1 %A A138839 _Omar E. Pol_, Apr 02 2008