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 A100645 #14 Oct 09 2013 08:59:32
%S A100645 1,3,2,25,9,49,-464,27,-16175,-3237113,-105387,-1737125143,-770720657,
%T A100645 -25881785,-1997012608,-135505859252213,-214182958293,
%U A100645 -528114253960241,-19467909708875,-595278405326437,-66462260889140083,-180690496141440384775397,-1610254561193224
%N A100645 Numerator of Cotesian number C(n,2).
%D A100645 Charles Jordan, Calculus of Finite Differences, Chelsea 1965, p. 513.
%H A100645 Vincenzo Librandi, <a href="/A100645/b100645.txt">Table of n, a(n) for n = 2..100</a>
%e A100645 1/6, 3/8, 2/15, 25/144, 9/280, 49/640, -464/14175, 27/2240, -16175/199584, -3237113/87091200, -105387/875875, -1737125143/22353408000, -770720657/5003856000, -25881785/229605376, ... = A100645/A100646 = A002179/A002176 (the latter not being in lowest terms)
%t A100645 cn[n_, 0] := Sum[n^j*StirlingS1[n, j]/(j+1), {j, 1, n+1}]/n!; cn[n_, n_] := cn[n, 0]; cn[n_, k_] := 1/n!*Binomial[n, k]*Sum[n^(j+m)*StirlingS1[k, j]* StirlingS1[n-k, m]/((m+1)*Binomial[j+m+1, m+1]), {m, 1, n}, {j, 1, k+1}]; a[n_] := Numerator[cn[n, 2]]; Table[a[n], {n, 2, 24}] (* _Jean-François Alcover_, Oct 08 2013 *)
%Y A100645 Cf. A100646.
%Y A100645 See A002176 for further references. A diagonal of A100640/A100641.
%K A100645 sign,frac
%O A100645 2,2
%A A100645 _N. J. A. Sloane_, Dec 05 2004