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 A338465 #9 Feb 05 2021 06:11:24
%S A338465 1,0,2,0,6,5,20,42,70,261,297,1430,1584,7293,9634,35945,60150,176596,
%T A338465 366401,886977,2150421,4624410,12205074,25065216,67616872,139894305,
%U A338465 369551925,793214982,2011977414,4517758504,10992821055,25669627965,60531471286,145112506352
%N A338465 Number of ways to write 2*n as an ordered sum of n nonzero triangular numbers.
%C A338465 Also number of ways to write n as an ordered sum of n nonnegative numbers one less than a triangular number.
%H A338465 Alois P. Heinz, <a href="/A338465/b338465.txt">Table of n, a(n) for n = 0..2000</a>
%F A338465 a(n) = [x^(2*n)] (theta_2(sqrt(x)) / (2 * x^(1/8)) - 1)^n, where theta_2() is the Jacobi theta function.
%F A338465 a(n) = [x^n] (Sum_{k>=0} x^(k*(k + 3)/2))^n.
%t A338465 Table[SeriesCoefficient[(EllipticTheta[2, 0, Sqrt[x]]/(2 x^(1/8)) - 1)^n, {x, 0, 2 n}], {n, 0, 33}]
%Y A338465 Cf. A000096, A000217, A106337, A298858, A319799.
%K A338465 nonn
%O A338465 0,3
%A A338465 _Ilya Gutkovskiy_, Jan 31 2021