# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/

Search: id:a371621
Showing 1-1 of 1

%I A371621 #18 Apr 04 2024 10:27:05
%S A371621 1,1,1,2,4,-10,-130,-840,-5880,-36960,-142800,184800,12843600,
%T A371621 229429200,3035432400,31615584000,258306048000,943422480000,
%U A371621 -26673126480000,-902769547680000,-18345450483360000,-300501672831360000,-3983084426280960000
%N A371621 Expansion of e.g.f. 1 / (1 - x + x^2/2 - x^3/3 + x^4/4).
%F A371621 a(n) = n * a(n-1) - n * (n-1) * a(n-2) / 2 + n * (n-1) * (n-2) * a(n-3) / 3 - n * (n-1) * (n-2) * (n-3) * a(n-4) / 4.
%t A371621 nmax = 22; CoefficientList[Series[1/(1 - x + x^2/2 - x^3/3 + x^4/4), {x, 0, nmax}], x] Range[0, nmax]!
%t A371621 a[0] = a[1] = a[2] = 1; a[3] = 2; a[n_] := a[n] = n a[n - 1] - n (n - 1) a[n - 2]/2 + n (n - 1) (n - 2) a[n - 3]/3 - n (n - 1) (n - 2) (n - 3) a[n - 4]/4; Table[a[n], {n, 0, 22}]
%Y A371621 Cf. A006252, A009775, A217260, A355294, A371605.
%K A371621 sign
%O A371621 0,4
%A A371621 _Ilya Gutkovskiy_, Apr 01 2024

# Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE