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 A232108 #9 Nov 19 2013 04:00:49 %S A232108 1,2,4,14,90,438,3151,24390,204156,1833212,17301306,175936764, %T A232108 1870247133,20872753540,243478609605,2957875659062,37319273049382, %U A232108 487266892836348,6574891059415183,91475580555526776,1309960647920094337,19278546942842385994,291167370195970990704,4507447478297070537800 %N A232108 a(n) = [x^(n*(n+1)/2)] G(x)^(n+1) where G(x) = Sum_{n>=0} x^(n*(n+1)/2). %H A232108 Paul D. Hanna, <a href="/A232108/b232108.txt">Table of n, a(n) for n = 0..100</a> %e A232108 Let G(x) = 1 + x + x^3 + x^6 + x^10 + x^15 + x^21 + x^28 + x^36 +... %e A232108 then a(n) = the coefficient of x^(n*(n+1)/2) in G(x)^n. %e A232108 Coefficients of x^k in powers of G(x)^n begin: %e A232108 n\k...0...1..2..3..4..5...6...7...8...9..10..11..12...13..14...15...16... %e A232108 n=1: [(1),1, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0,...]; %e A232108 n=2: [1, (2),1, 2, 2, 0, 3, 2, 0, 2, 2, 2, 1, 2, 0, 2, 4,...]; %e A232108 n=3: [1, 3, 3,(4),6, 3, 6, 9, 3, 7, 9, 6, 9, 9, 6, 6, 15,...]; %e A232108 n=4: [1, 4, 6, 8,13,12,(14),24, 18, 20, 32, 24, 31, 40, 30, 32, 48,...]; %e A232108 n=5: [1, 5,10,15,25,31, 35, 55, 60, 60,(90),90, 95, 135,125, 126, 170,...]; %e A232108 n=6: [1, 6,15,26,45,66, 82,120,156,170,231,276,290, 390,435,(438),561,...]; ... %e A232108 the coefficients in parenthesis form the initial terms of this sequence. %o A232108 (PARI) {a(n)=local(G=sum(m=0, n+1, x^(m*(m+1)/2))+x*O(x^(n*(n+1)/2))); polcoeff(G^(n+1), n*(n+1)/2)} %o A232108 for(n=0,30,print1(a(n),", ")) %Y A232108 Cf. A196010. %K A232108 nonn %O A232108 0,2 %A A232108 _Paul D. Hanna_, Nov 18 2013