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 A190187 #20 Dec 30 2017 03:27:55
%S A190187 1,1,3,6,15,90,630,720,45360,64800,4989600,59875200,778377600,
%T A190187 1556755200,163459296000,373621248000,44460928512000,800296713216000,
%U A190187 15205637551104000,3949516247040000,6386367771463680000,20071441567457280000,3231502092360622080000,5965850016665763840000,1938901255416373248000000,7201633234403672064000000
%N A190187 Denominator of expression W_n occurring in analysis of bubble sort.
%D A190187 D. E. Knuth, The Art of Computer Programming, Vol. 3, Section 5.2.2, p. 129.
%H A190187 G. C. Greubel, <a href="/A190187/b190187.txt">Table of n, a(n) for n = 1..450</a>
%F A190187 W_n = Sum_{r=0..(n-1)}( Sum_{s=(r+1)..n} s!*r^(n-s) )/n!.
%F A190187 W_n = denominator(A190194(n)/n!).
%e A190187 1, 2, 10/3, 29/6, 97/15, 739/90, 6331/630, 8617/720, 633127/45360, 1037497/64800, ...
%p A190187 W:=proc(n) local t1,r,s;
%p A190187 t1:=add( add(s!*r^(n-s), s=r+1..n), r=0..n-1);
%p A190187 t1/n!;
%p A190187 end;
%t A190187 Denominator[Table[n! + Sum[ Sum[s!*k^(n - s), {s, k + 1, n}], {k, 1, n - 1}]/n!, {n, 1, 50}]] (* _G. C. Greubel_, Dec 28 2017 *)
%o A190187 (PARI) for(n=1,30, print1(denominator(1 + sum(k=1,n-1, sum(s=k+1, n, s!*k^(n-s)))/n!), ", ")) \\ _G. C. Greubel_, Dec 28 2017
%Y A190187 Cf. A190186.
%K A190187 nonn,frac
%O A190187 1,3
%A A190187 _N. J. A. Sloane_, May 05 2011