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A052680 Expansion of e.g.f. (1-2*x)/(1-4*x+2*x^2). 1
1, 2, 12, 120, 1632, 27840, 570240, 13628160, 372234240, 11437977600, 390516940800, 14666390323200, 600890263142400, 26670379902566400, 1274817218759884800, 65287473566515200000, 3566486043252228096000 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,2
LINKS
FORMULA
E.g.f.: (1 - 2*x)/(1 - 4*x + 2*x^2).
D-finite with Recurrence: a(0)=1, a(1)=2, a(n+2) = 4*(n+2)*a(n+1) - 2*(2 +3*n +n^2)*a(n).
a(n) = (n!/2)*Sum_{alpha=RootOf(1 - 4*Z + 2*Z^2)} alpha^(-n).
a(n) = n!*A006012(n). - R. J. Mathar, Nov 27 2011
From G. C. Greubel, Jun 10 2022: (Start)
a(2*n) = (2*n)! * 2^(n-1)*A002203(2*n).
a(2*n+1) = (2*n+1)! * 2^(n+1)*A000129(2*n+1).
a(n) = 2^(n/2) * n! * ChebyshevT(n, sqrt(2)). (End)
MAPLE
spec := [S, {S=Sequence(Union(Z, Prod(Z, Sequence(Union(Z, Z)))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
MATHEMATICA
With[{nn=20}, CoefficientList[Series[(1-2x)/(1-4x+2x^2), {x, 0, nn}], x] Range[ 0, nn]!] (* Harvey P. Dale, Jan 28 2019 *)
Table[n!*2^(n/2)*ChebyshevT[n, Sqrt[2]], {n, 0, 50}] (* G. C. Greubel, Jun 10 2022 *)
PROG
(Magma) [Factorial(n)*(&+[Binomial(n, 2*k)*2^(n-k): k in [0..Floor(n/2)]]): n in [0..30]]; // G. C. Greubel, Jun 10 2022
(SageMath) [2^(n/2)*factorial(n)*chebyshev_T(n, sqrt(2)) for n in (0..50)] # G. C. Greubel, Jun 10 2022
CROSSREFS
Sequence in context: A189981 A326000 A245067 * A096317 A226760 A226758
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
STATUS
approved

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Last modified March 1 19:16 EST 2024. Contains 370443 sequences. (Running on oeis4.)