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 A129731 #11 Nov 11 2016 20:02:09
%S A129731 1,3,15,105,1470,42630,1364160,75028800,3676411200,272054428800
%N A129731 Each term is the previous term times the number of letters in the previous number, as conventionally spelled out in English.
%C A129731 Multiplicative analog of A060403.
%F A129731 a(0) = 1; a(n+1) = a(n) * A005589(a(n)). a(0) = 1; a(n+1) = PRODUCT[i=1..n] A005589(a(i)).
%e A129731 a(1) = 1.
%e A129731 a(2) = 1 * A060403(1) = 1 * LettersIn("one") = 1*3 = 3.
%e A129731 a(3) = 3 * A060403(2) = 3 * LettersIn("three") = 3*5 = 15.
%e A129731 a(4) = 15 * A060403(3) = 15 * LettersIn("fifteen") = 15*7 = 105.
%e A129731 a(10) = 74 * A060403(a(9)) = 74 * LettersIn("three billion six hundred seventysix million four hundred eleven thousand two hundred") = 1364160 * 55 * 49 * 74 = 272054 28800 = 2^7 * 3 * 5^2 * 7^4 * 11 * 29 * 37.
%Y A129731 Cf. A005589, A060403.
%K A129731 easy,nonn,word,dumb,less
%O A129731 1,2
%A A129731 _Jonathan Vos Post_, May 12 2007, May 22 2007