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 A107874 #5 Oct 05 2019 10:42:46
%S A107874 1,4,15,84,715,8568,134596,2629575,61523748,1677106640,52179482355,
%T A107874 1823810410032,70724320184700,3012192716517082,139737927523546800,
%U A107874 7012067478708989884,378371310857796292200,21843987843214746108900
%N A107874 Column 0 of triangle A107873; a(n) = C( n*(n-1)/2 + n+3, n).
%t A107874 Table[Binomial[(n(n-1))/2+n+3,n],{n,0,20}] (* _Harvey P. Dale_, Oct 05 2019 *)
%o A107874 (PARI) a(n)=binomial(n*(n-1)/2+n+3,n)
%Y A107874 Cf. A107873, A107875.
%K A107874 nonn
%O A107874 0,2
%A A107874 _Paul D. Hanna_, Jun 04 2005