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 A057003 #16 Jul 13 2021 09:42:26
%S A057003 1,6,120,5040,360360,39070080,5967561600,1220096908800,
%T A057003 321570878428800,106137499051584000,42873948150095462400,
%U A057003 20803502274492921984000,11938961126118491232768000,7998487694738166709923840000,6185983879158893706209144832000
%N A057003 Write the natural numbers in groups: 1; 2,3; 4,5,6; 7,8,9,10; ... and multiply the members of each group.
%C A057003 Each group begins with a triangular number + 1 and proceeds until the next triangular number.
%H A057003 Alois P. Heinz, <a href="/A057003/b057003.txt">Table of n, a(n) for n = 1..200</a>
%F A057003 (n (n + 1)/2)!/((n - 1) n /2)!.
%F A057003 a(n) ~ n^(2*n)/2^n. - _Vaclav Kotesovec_, Jul 13 2021
%p A057003 a:= n-> binomial(n*(n+1)/2, n) * n!:
%p A057003 seq(a(n), n=1..20); # _Alois P. Heinz_, Aug 17 2012
%t A057003 Table[(n (n + 1)/2)!/((n - 1) n /2)!, {n, 1, 15}]
%t A057003 With[{nn=15},Times@@@TakeList[Range[(nn(nn+1))/2],Range[nn]]] (* Requires Mathematica version 11 or later *) (* _Harvey P. Dale_, Sep 21 2017 *)
%Y A057003 Cf. A006003.
%K A057003 nonn
%O A057003 1,2
%A A057003 _Robert G. Wilson v_, Sep 09 2000