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 A107974 #5 Jul 30 2015 23:01:20
%S A107974 3,6,12,13,15,16,19,20,25,26,32,33,42,44,44,46,51,53,59,62,64,67,70,
%T A107974 74,76,80,84,88,92,96,102,107,108,113,116,121,130,136,138,144,148,154,
%U A107974 161,168,168,175,179,186,192,200,200,208,212,220,228,237,239,248,254,255
%N A107974 First differences give the same sequence written as a string of individual digits.
%e A107974 3.6.12.13.15.16.19.20.25 ... <- sequence
%e A107974 .3.6..1..2..1..3..1..5 ... <- first differences are the sequence's digits.
%t A107974 a[1] = 3; a[n_] := a[n] = a[n - 1] + Flatten[ Table[ IntegerDigits[ a[i]], {i, n - 1}]][[n - 1]]; Table[ a[n], {n, 60}] (* _Robert G. Wilson v_, Jun 15 2005 *)
%Y A107974 Cf. A100787, A107974, A107975, A107976, A107977 for "seeds" 1, 3, 5, 7 and 9.
%K A107974 base,easy,nonn
%O A107974 1,1
%A A107974 _Eric Angelini_, Jun 12 2005
%E A107974 Edited and extended by _Robert G. Wilson v_, Jun 15 2005