A330436 a(n) = n * n!! - Sum_{k=1..n-1} k!! * a(n-k).
1, 3, 4, 19, 31, 168, 323, 1859, 4072, 24403, 59423, 368488, 980123, 6275139, 17998264, 118858755, 364059999, 2478263856, 8045642683, 56418223739, 192980878976, 1392909382923, 4995715059111, 37083230363840, 138896979832131, 1059335618366171
Offset: 1
Keywords
Programs
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Mathematica
a[n_] := a[n] = n n!! - Sum[k!! a[n - k], {k, 1, n - 1}]; Table[a[n], {n, 1, 26}] nmax = 26; CoefficientList[Series[Log[Sum[k!! x^k, {k, 0, nmax}]], {x, 0, nmax}], x] Range[0, nmax] // Rest
Formula
L.g.f.: log(Sum_{k>=0} k!! * x^k).
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