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A228484 a(n) = 2^n*(3*n)!/(n!*(2*n)!). 2
1, 6, 60, 672, 7920, 96096, 1188096, 14883840, 188280576, 2399654400, 30766095360, 396363202560, 5126871859200, 66538909237248, 866061993246720, 11300615801536512, 147773778404769792, 1936073567335219200, 25408660721789829120, 333963051307735449600 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Oblique diagonal of the Pell-Jacobsthal triangle A013609. Its mirror diagonal is A006588.

Asymptotic approximation of a(n) ~ C*(13.5)^n/sqrt(n) with C = (1/2)*sqrt(3/Pi) = A137209.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..200

FORMULA

a(n) = 2^n*A005809(n).

a(n) = A013609(3*n, n).

a(n) = A006588(n)/2^n.

a(n) = (2*n+1)*A153231(n).

MAPLE

a := n -> 2^n*binomial(3*n, n): seq(a(n), n=0..16);

MATHEMATICA

Table[2^n (3 n)!/(n! (2 n)!), {n, 0, 20}] (* Vincenzo Librandi, Aug 24 2013 *)

PROG

(MAGMA) [2^n*Factorial(3*n)/(Factorial(n)*Factorial(2*n)): n in [0..20]]; // Vincenzo Librandi, Aug 24 2013

CROSSREFS

Cf. A013609, A006588.

Sequence in context: A295503 A106259 A085364 * A232969 A232246 A086984

Adjacent sequences:  A228481 A228482 A228483 * A228485 A228486 A228487

KEYWORD

nonn,easy

AUTHOR

Johannes W. Meijer, Aug 22 2013

EXTENSIONS

More terms from Vincenzo Librandi, Aug 24 2013

STATUS

approved

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Last modified August 23 22:45 EDT 2019. Contains 326254 sequences. (Running on oeis4.)