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 A139097 #13 Mar 31 2017 20:48:08 %S A139097 0,4,8,13,21,30,36,45,54,63,73,85,95,105,119,137,158,178,200,211,227, %T A139097 248,268,288,309,325,347,369,390,408,424,445,465,485,506,520,537,559, %U A139097 579,601,614,632,651,669,688,709,725,747,769,790,808,825,847,869,890,908,924,945,965,985,1006,1020,1037,1059 %N A139097 Form a sequence of words as follows: look to the left, towards the beginning of the sequence and write down the number of letters you see; repeat; then replace the words with the corresponding numbers. %C A139097 The sequence of words is: zero, four, eight, thirteen, twenty-one, thirty, ... (in American English). %C A139097 Hyphens and spaces are not counted. %C A139097 This is an English version of the sequence in A139121. %C A139097 a(0) = 0, a(n+1) = a(n) + A005589(a(n)). - _Jonathan Vos Post_, Jun 15 2008 %D A139097 E. Angelini, "Jeux de suites", in Dossier Pour La Science, pp. 32-35, Volume 59 (Jeux math'), April/June 2008, Paris. %H A139097 M. F. Hasler, <a href="/A139097/b139097.txt">Table of n, a(n) for n = 0..423</a> %e A139097 The second word is "four" (and so a(2)=4), because at the end of the first word we can see four letters to the left. %Y A139097 Cf. A005589. See A060403 and A139121 for other versions. %K A139097 nonn,word,easy %O A139097 0,2 %A A139097 _Jonathan Vos Post_, May 12 2007 %E A139097 Edited by _N. J. A. Sloane_, Jun 08 2008 %E A139097 More terms from _M. F. Hasler_ and _R. J. Mathar_, Jun 15 2008