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A084261
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A binomial transform of factorial numbers.
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11
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1, 1, 2, 4, 9, 21, 52, 134, 361, 1009, 2926, 8768, 27121, 86373, 282864, 950866, 3277169, 11564353, 41739130, 153919324, 579411641, 2224535125, 8703993420, 34681783422, 140637608089, 580019801201, 2431509498406, 10355296410712
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OFFSET
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0,3
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COMMENTS
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Binomial transform of A000142 (with interpolated zeros).
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LINKS
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FORMULA
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a(n) = Sum_{k=0..floor(n/2)} C(n, 2k)*k!.
a(n) = Sum_{k=0..n} C(n, k)*(k/2)!*((1+(-1)^k)/2) .
E.g.f.: exp(x)*(1+sqrt(Pi)/2*x*exp(x^2/4)*erf(x/2)). - Vladeta Jovovic, Sep 25 2003
O.g.f.: A(x) = 1/(1-x-x^2/(1-x-x^2/(1-x-2*x^2/(1-x-2*x^2/(1-x-3*x^2/(1-... -x-[(n+1)/2]*x^2/(1- ...))))))) (continued fraction). - Paul D. Hanna, Jan 17 2006
a_n ~ (1/2) * sqrt(Pi*n/e)*(n/2)^(n/2)*exp(-n/2 + sqrt(2n)). - Cecil C Rousseau (ccrousse(AT)memphis.edu), Mar 14 2006: (cf. A002896).
Conjecture: 2*a(n) -4*a(n-1) +(-n+2)*a(n-2) +(n-2)*a(n-3)=0. - R. J. Mathar, Nov 30 2012
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MATHEMATICA
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Table[Sum[Binomial[n, 2*k]*k!, {k, 0, Floor[n/2]}], {n, 0, 50}] (* G. C. Greubel, Jan 24 2017 *)
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PROG
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(PARI) for(n=0, 50, print1(sum(k=0, floor(n/2), binomial(n, 2*k)*k!), ", ")) \\ G. C. Greubel, Jan 24 2017
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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