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 A065355 #31 Feb 20 2024 11:17:18
%S A065355 1,0,0,2,14,86,566,4166,34406,316646,3219686,35878886,435046886,
%T A065355 5704064486,80428314086,1213746099686,19521187251686,333363035571686,
%U A065355 6024361885107686,114864714882483686,2304476522241459686
%N A065355 a(n) = n! - Sum_{k=0..n-1} k!.
%C A065355 For n > 1, the factorial base representation of a(n) is {n-2, n-3, ..., 1, 0}, i.e., the numbers 0..(n-2) in descending order. - _Amiram Eldar_, Apr 24 2021
%H A065355 Harry J. Smith, <a href="/A065355/b065355.txt">Table of n, a(n) for n = 0..100</a>
%F A065355 a(n) = A000142(n) - A003422(n). - _Darío Clavijo_, Feb 16 2024
%t A065355 Table[ n! - Sum[k!, {k, 0, n - 1} ], {n, 0, 20} ]
%o A065355 (PARI) a(n) = n! - sum(k=0, n-1, k!); \\ _Harry J. Smith_, Oct 17 2009
%o A065355 (Python)
%o A065355 from sympy import factorial
%o A065355 left_factorial = lambda n: left_factorial(n - 1) + factorial(n - 1) if n > 0 else 0
%o A065355 a = lambda n: factorial(n) - left_factorial(n) # _Darío Clavijo_, Feb 16 2024
%Y A065355 Cf. A000142, A003422, A007623.
%K A065355 easy,nonn
%O A065355 0,4
%A A065355 _Floor van Lamoen_, Oct 31 2001