A051580 a(n) = (2*n+6)!!/6!!, related to A000165 (even double factorials).

1, 8, 80, 960, 13440, 215040, 3870720, 77414400, 1703116800, 40874803200, 1062744883200, 29756856729600, 892705701888000, 28566582460416000, 971263803654144000, 34965496931549184000, 1328688883398868992000

Offset

0,2

Comments

Row m=6 of the array A(3; m,n) := (2*n+m)!!/m!!, m >= 0, n >= 0.

Links

G. C. Greubel, Table of n, a(n) for n = 0..400

A. N. Stokes, Continued fraction solutions of the Riccati equation, Bull. Austral. Math. Soc. Vol. 25 (1982), 207-214.

Formula

a(n) = (2*n+6)!!/6!!.

E.g.f.: 1/(1-2*x)^4.

a(n) = n!*2^(n-4)/3, n>=3. - Zerinvary Lajos, Sep 23 2006

G.f.: G(0)/2, where G(k)= 1 + 1/(1 - x/(x + 1/(2*k+8)/G(k+1))); (continued fraction). - Sergei N. Gladkovskii, Jun 02 2013

From Peter Bala, May 26 2017: (Start)

a(n+1) = (2*n + 8)*a(n) with a(0) = 1.

O.g.f. satisfies the Riccati differential equation 2*x^2*A(x)' = (1 - 8*x)*A(x) - 1 with A(0) = 1.

G.f. as an S-fraction: A(x) = 1/(1 - 8*x/(1 - 2*x/(1 - 10*x/(1 - 4*x/(1 - 12*x/(1 - 6*x/(1 - ... - (2*n + 6)*x/(1 - 2*n*x/(1 - ...))))))))) (by Stokes 1982).

Reciprocal as an S-fraction: 1/A(x) = 1/(1 + 8*x/(1 - 10*x/(1 - 2*x/(1 - 12*x/(1 - 4*x/(1 - 14*x/(1 - 6*x/(1 - ... - (2*n + 8)*x/(1 - 2*n*x/(1 - ...)))))))))). (End)

From Amiram Eldar, Dec 11 2022: (Start)

Sum_{n>=0} 1/a(n) = 48*sqrt(e) - 78.

Sum_{n>=0} (-1)^n/a(n) = 30 - 48/sqrt(e). (End)

Maple

seq( mul(2*j+6, j=1..n), n=0..20); # G. C. Greubel, Nov 11 2019

Mathematica

Table[2^n*Pochhammer[4, n], {n, 0, 20}] (* G. C. Greubel, Nov 11 2019 *)
Table[(2n+6)!!/6!!, {n, 0, 20}] (* Harvey P. Dale, Mar 03 2022 *)

Prog

(PARI) vector(20, n, prod(j=1, n-1, 2*j+6) ) \\ G. C. Greubel, Nov 11 2019
(Magma) [1] cat [(&*[2*j+6: j in [1..n]]): n in [1..20]]; // G. C. Greubel, Nov 11 2019
(Sage) [product( (2*j+6) for j in (1..n)) for n in (0..20)] # G. C. Greubel, Nov 11 2019
(GAP) List([0..20], n-> Product([1..n], j-> 2*j+6) ); # G. C. Greubel, Nov 11 2019

Crossrefs

Cf. A000165, A001147(n+1), A002866(n+1), A051577, A051578, A051579 (rows m=0..5), A051581, A051582, A051583.

Sequence in context: A269796 A328128 A053175 * A228658 A234596 A060375

Adjacent sequences: A051577 A051578 A051579 * A051581 A051582 A051583

Keyword

easy,nonn

Author

Wolfdieter Lang

Status

approved