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 A386879 #8 Aug 06 2025 11:53:16
%S A386879 1,0,1,10,126,2002,38760,888030,23535820,708930508,23930713170,
%T A386879 895068996640,36749279048405,1643385429346680,79515468511191440,
%U A386879 4139207762053520646,230672804560960311000,13703037308872895467960,864424422377992704918690,57711135174726478041405270,4065392394346039279040037520
%N A386879 a(n) = [x^n] 1/(1 - x)^(n*(n-1)/2).
%F A386879 a(n) ~ exp(n) * n^(n - 1/2) / (sqrt(Pi) * 2^(n + 1/2)).
%F A386879 For n > 0, a(n) = binomial(n*(n+1)/2, n) * (n-1)/(n+1).
%t A386879 Table[SeriesCoefficient[1/(1-x)^(n*(n-1)/2), {x, 0, n}], {n, 0, 25}]
%t A386879 Join[{1}, Table[Binomial[n*(n+1)/2, n] * (n-1) / (n+1), {n, 1, 25}]]
%Y A386879 Cf. A014068, A054688, A116508, A177234, A386880.
%K A386879 nonn
%O A386879 0,4
%A A386879 _Vaclav Kotesovec_, Aug 06 2025