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 A109336 #4 Mar 31 2012 14:11:37 %S A109336 1,2,33,444444444444444444444444444444444 %N A109336 "Que sera, sera" sequence: self-describing sequence where a(n) gives the number of n+1's which will be concatenated to form a(n+1); starting with a(1) = 1. %F A109336 a(1) = 1. For n > 1, let k = floor(1+log_10(n)); then a(n) = n*(10^(k*a(n-1))-1)/(10^k-1). %e A109336 a(1) says: there will be one 2 in a(2). %e A109336 a(2)=2 because a(1) said so; and a(2)=2 says: there will be two 3's in a(3). %e A109336 a(3)=33 because a(2) said so; and also a(3) says: there will be thirty three 4's in a(4). %e A109336 Therefore a(4)= 444444444444444444444444444444444 (33 times the digit 4). %e A109336 And a(5)= 555555555555555...555 (with 444444444444444444444444444444444 5's). %Y A109336 Cf. A001462, A001463, A103320, A102357, A076782. %K A109336 base,nonn %O A109336 1,2 %A A109336 _Alexandre Wajnberg_, Aug 23 2005 %E A109336 Formula corrected to handle n>9 also by _Rick L. Shepherd_, Mar 22 2009