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 A020547 #36 Jul 05 2025 18:43:47
%S A020547 0,0,2,30,552,14280,517680,25396560,1625662080,131681531520,
%T A020547 13168185811200,1593350882323200,229442532323558400,
%U A020547 38775788037405619200,7600054456464819148800,1710012252722891749632000,437763136697374129754112000
%N A020547 2nd Euler polynomial x^2 - x evaluated at x=n!.
%H A020547 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/EulerPolynomial.html">Euler Polynomial</a>.
%F A020547 a(n) = n!*(n!-1). - _Mark van Hoeij_, May 13 2013
%F A020547 a(n) = A000142(n)*A000142(n-1). - _Michel Marcus_, Apr 15 2015
%F A020547 a(n) = 2*(A055555(n) - A000142(n)). - _J.S. Seneschal_, Jul 01 2025
%t A020547 Table[n! (n! - 1), {n, 0, 20}] (* _Vincenzo Librandi_, Apr 15 2015 *)
%o A020547 (PARI) vector(20, n, n--; (n!)^2-n!) \\ _Michel Marcus_, Apr 15 2015
%o A020547 (Magma) [Factorial(n)*(Factorial(n)-1): n in [0..30]]; // _Vincenzo Librandi_, Apr 15 2015
%Y A020547 Cf. A000142 (n!), A055555.
%K A020547 nonn,easy
%O A020547 0,3
%A A020547 _Simon Plouffe_