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 A121945 #8 Sep 08 2022 08:45:27
%S A121945 1,3,11,69,929,30273,2591057,614059329,423463272449,907403624202753,
%T A121945 6082394749206781697,140440480114401911810049,
%U A121945 10845109029138237198786147329,3088811811740393517911301490890753,3220352134317904958924570965080200574977,12657255883388612328426763834234183884771442689
%N A121945 a(n) is the sum of the first n factorials in decreasing powers from n to 1. a(n) = Sum_{k = 1..n} k!^(n-k+1).
%H A121945 G. C. Greubel, <a href="/A121945/b121945.txt">Table of n, a(n) for n = 1..58</a>
%p A121945 seq(add(factorial(j)^(n-j+1), j=1..n), n=1..20); # _G. C. Greubel_, Oct 07 2019
%t A121945 Table[Sum[Factorial[i]^(n-i+1), {i, n}], {n, 20}]
%o A121945 (PARI) vector(20, n, sum(j=1, n, (j!)^(n-j+1)) ) \\ _G. C. Greubel_, Oct 07 2019
%o A121945 (Magma) [(&+[Factorial(j)^(n-j+1): j in [1..n]]): n in [1..20]]; // _G. C. Greubel_, Oct 07 2019
%o A121945 (Sage) [sum(factorial(j)^(n-j+1) for j in (1..n)) for n in (1..20)] # _G. C. Greubel_, Oct 07 2019
%o A121945 (GAP) List([1..20], n-> Sum([1..n], j-> Factorial(j)^(n-j+1)) ); # _G. C. Greubel_, Oct 07 2019
%Y A121945 Similar to A003101 = Sum_{k = 1..n} (n-k+1)^k - only with inserted factorials.
%K A121945 nonn
%O A121945 1,2
%A A121945 _Tanya Khovanova_, Sep 03 2006
%E A121945 More terms from _G. C. Greubel_, Oct 07 2019