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 A298858 #5 Feb 16 2025 08:33:53
%S A298858 1,1,0,0,4,11,86,777,4670,36075,279482,2345201,21247326,197065752,
%T A298858 1983741228,20769081251,228078253168,2604226354265,30880251148086,
%U A298858 379415992755572,4818158748326064,63116999199457944,851467484377802094,11811530978240316682,168243449082524484856
%N A298858 Number of ordered ways of writing n-th triangular number as a sum of n nonzero triangular numbers.
%H A298858 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TriangularNumber.html">Triangular Number</a>
%H A298858 <a href="/index/Pol#polygonal_numbers">Index to sequences related to polygonal numbers</a>
%F A298858 a(n) = [x^(n*(n+1)/2)] (Sum_{k>=1} x^(k*(k+1)/2))^n.
%e A298858 a(4) = 4 because fourth triangular number is 10 and we have [3, 3, 3, 1], [3, 3, 1, 3], [3, 1, 3, 3] and [1, 3, 3, 3].
%t A298858 Table[SeriesCoefficient[(EllipticTheta[2, 0, Sqrt[x]]/(2 x^(1/8)) - 1)^n, {x, 0, n (n + 1)/2}], {n, 0, 24}]
%Y A298858 Cf. A000217, A007294, A023361, A024940, A072964, A106337, A196010, A288126, A298329, A298330.
%K A298858 nonn
%O A298858 0,5
%A A298858 _Ilya Gutkovskiy_, Jan 27 2018