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A151817 a(n) = 2*(2*n)!/n!. 2
2, 4, 24, 240, 3360, 60480, 1330560, 34594560, 1037836800, 35286451200, 1340885145600, 56317176115200, 2590590101299200, 129529505064960000, 6994593273507840000, 405686409863454720000, 25152557411534192640000, 1660068789161256714240000, 116204815241287969996800000 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

Row sums of A155951.

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..364

FORMULA

(Possible closed form for all terms given) a(n) = 2^(2*n-1)* Pochhammer[1/2, -1 + n] = 2^(2*n-1)*(Gamma(1/2+n-1))/(Gamma(1/2)) = 2^(2*n-1)*(Gamma(n-1/2))/sqrt(pi) (Possible recurrence relation: for all terms given) a(n+1) = 2*(2*n-1)*a(n). - Alexander R. Povolotsky, Jul 06 2009

E.g.f.: 2/(1-4*x)^(1/2).- Sergei N. Gladkovskii, Dec 05 2011

G.f.: G(0), where G(k)= 1 + 1/(1 - x*(4*k+2)/(x*(4*k+2) + 1/G(k+1))); (continued fraction). - Sergei N. Gladkovskii, Jun 04 2013

a(n) = A052718(n+1), n>0.

a(n) = 2*A001813(n). - R. J. Mathar, Mar 12 2017

MATHEMATICA

Table[2*(2*n)!/n!, {n, 0, 50}] (* G. C. Greubel, Feb 21 2017 *)

PROG

(PARI) a(n)=2*(2*n)!/n! \\ Charles R Greathouse IV, Dec 05 2011

CROSSREFS

Cf. A052718.

Sequence in context: A141307 A190655 A038049 * A265937 A038058 A062531

Adjacent sequences:  A151814 A151815 A151816 * A151818 A151819 A151820

KEYWORD

nonn,easy

AUTHOR

Roger L. Bagula, Jan 31 2009

EXTENSIONS

Typo in definition corrected by N. J. A. Sloane, Jul 12 2009

New name from Sergei N. Gladkovskii, Dec 05 2011

STATUS

approved

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Last modified May 24 17:09 EDT 2019. Contains 323533 sequences. (Running on oeis4.)