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 A126973 #7 May 13 2013 01:48:41 %S A126973 1,10,13,23,1233,33999999999999999 %N A126973 a(n+1) is the smallest integer greater than a(n) such that the sum of the squares of its decimal digits is equal to a(n). %e A126973 10 --> 1^2+0^2 = 1+0 =1 %e A126973 13 --> 1^2+3^2 = 1+9 = 10 %e A126973 23 --> 2^2+3^2 = 4+9 =13 %e A126973 1233 --> 1^2+2^2+3^3+3^2 = 1+4+9+9 = 23 %e A126973 33999999999999999 = 3^2*2 + 9^2*15 = 1233 %Y A126973 Cf. A001273, A053612. %K A126973 nonn,base %O A126973 1,2 %A A126973 _Paolo P. Lava_ and _Giorgio Balzarotti_, Mar 20 2007; corrected Mar 23 2007 %E A126973 Next term is greater than 10^419753086419753. [From _Charles R Greathouse IV_, Nov 13 2010]