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A074143
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a(1) = 1; a(n) = n * sum {a(k) | k < n}.
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7
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1, 2, 9, 48, 300, 2160, 17640, 161280, 1632960, 18144000, 219542400, 2874009600, 40475635200, 610248038400, 9807557760000, 167382319104000, 3023343138816000, 57621363351552000, 1155628453883904000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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LINKS
| Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets
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FORMULA
| a(n) = n^2*a(n-1)/(n-1) for n > 2.
a(n) = n*ceiling[n!/2] = n*A001710(n-1) = A001710(n+1)-A001710(n) = ceiling[A001563(n)/2] - Henry Bottomley (se16(AT)btinternet.com), Nov 27 2002
a(n) = ((n+1)!-n!)/2 for n > 1. - Vladimir Joseph Stephan Orlovsky, Apr 03 2011
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MAPLE
| seq(sum(mul(j, j=3..n), k=1..n), n=1..19); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Jun 01 2007
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MATHEMATICA
| Join[{1}, Table[((n+1)!-n!)/2, {n, 2, 30}]] (*From Vladimir Joseph Stephan Orlovsky, Apr 03 2011*)
a[1] = 1; a[n_] := a[n] = n*Sum[a[k], {k, n-1}]; Array[a, 20] (* T. D. Noe, Apr 05 2011 *)
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CROSSREFS
| Sequence in context: A118341 A171803 A100427 * A198892 A205571 A052826
Adjacent sequences: A074140 A074141 A074142 * A074144 A074145 A074146
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KEYWORD
| nonn
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Aug 28 2002
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EXTENSIONS
| More terms from Henry Bottomley (se16(AT)btinternet.com), Nov 27 2002
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