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A213168
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a(n) = n!/2 - (n-1)! - n + 2.
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2
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0, 0, 4, 33, 236, 1795, 15114, 141113, 1451512, 16329591, 199583990, 2634508789, 37362124788, 566658892787, 9153720575986, 156920924159985, 2845499424767984, 54420176498687983, 1094805903679487982, 23112569077678079981, 510909421717094399980
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OFFSET
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2,3
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COMMENTS
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LINKS
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FORMULA
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D-finite with recurrence: 2*(n-3)*a(n) - (2*n^2-6*n+4)*a(n-1)- 2*(n-3)*(n-2)^2 = 0. - Georg Fischer, Aug 25 2021
E.g.f.: 1/(2-2*x)+log(1-x)+(2-x)*exp(x). - Alois P. Heinz, Aug 25 2021
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MAPLE
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f:=gfun:-rectoproc({2*(n-3)*a(n) - (2*n^2-6*n+4)*a(n-1)- 2*(n-3)*(n-2)^2, a(2)=0, a(3)=0}, a(n), remember): map(f, [$2..22]); # Georg Fischer, Aug 25 2021
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MATHEMATICA
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Table[n!/2 - (n - 1)! - n + 2, {n, 2, 20}]
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PROG
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(Maxima) A213168(n):=n!/2-(n-1)!-n+2$
(Magma) [Factorial(n)/2-Factorial(n-1)-n+2: n in [2..25]]; // Vincenzo Librandi, Sep 09 2016
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CROSSREFS
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Cf. A200748 (considered as a triangular array).
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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