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 A138209 #2 Mar 30 2012 18:37:09
%S A138209 1,1,-3,24,-307,5367,-118836,3185098,-100249284,3625011513,
%T A138209 -148109085520,6748573217802,-339316619619180,18662532511884138,
%U A138209 -1114624766173882896,71841450181505629686,-4970296376217834343751,367389368833834570991097
%N A138209 G.f.: A(x) = 1 + x*(1 + x*(1 + x*(...(1 + x*(...)^(-3n) )...)^-9)^-6)^-3.
%e A138209 G.f.: A(x)=1+x/B(x)^3, B(x)=1+x/C(x)^6, C(x)=1+x/D(x)^9, D(x)=1+x/E(x)^12, ...
%e A138209 where A(x),B(x),C(x),... are the g.f. of the sequences given below.
%e A138209 A=[1,1,-3,24,-307,5367,-118836,3185098,-100249284,...];
%e A138209 B=[1,1,-6,75,-1352,31167,-867294,28172631,-1044977994,...];
%e A138209 C=[1,1,-9,153,-3567,102591,-3461832,133195605,-5737614804,...];
%e A138209 D=[1,1,-12,258,-7384,254955,-10139508,452535442,-22298633472,...];
%e A138209 E=[1,1,-15,390,-13235,533700,-24472908,1245207030,-69239330640,...];
%e A138209 F=[1,1,-18,549,-21552,994392,-51685074,2955896076,-183324843810,...]; ...
%o A138209 (PARI) {a(n)=local(A=1+x+x*O(x^n)); for(j=0, n-1, A=1+x*A^(-3*(n-j))); polcoeff(A, n)}
%Y A138209 Cf. A121587, A138213, A138210, A138208.
%K A138209 sign
%O A138209 0,3
%A A138209 _Paul D. Hanna_, Mar 06 2008