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A161581 a(n) = (3n)!/(n!(n+1)!(n+2)!). 3
21, 231, 3003, 43758, 692835, 11685817, 207157665, 3823000545, 72931087320, 1430571328200, 28734046963560, 589047962752980, 12292044987448215, 260543149635912165, 5599392250947235125, 121830987186399315825 (list; graph; refs; listen; history; text; internal format)
OFFSET

3,1

COMMENTS

3-d analog of the Catalan numbers A000108.

LINKS

Table of n, a(n) for n=3..18.

Eric Weisstein's World of Mathematics, Binomial Sums.

Eric Weisstein's World of Mathematics, Central Binomial Coefficient.

Eric Weisstein's World of Mathematics, Catalan Number.

FORMULA

a(n) = A006480(n)/((n+1)^2*(n+2)).

MAPLE

A161581 := proc(n) (3*n)!/n!/(n+1)!/(n+2)! ; end: seq(A161581(n), n=3..40) ; # R. J. Mathar, Jun 16 2009

a := proc (n) options operator, arrow: factorial(3*n)/(factorial(n)*factorial(n+1)*factorial(n+2)) end proc: seq(a(n), n = 3 .. 20); # Emeric Deutsch, Jun 14 2009

CROSSREFS

Cf. A000108, A006480.

Sequence in context: A022586 A321952 A125409 * A069601 A173347 A303968

Adjacent sequences:  A161578 A161579 A161580 * A161582 A161583 A161584

KEYWORD

nonn

AUTHOR

Alexander Adamchuk, Jun 14 2009

EXTENSIONS

Repetitions of information contained in other sequences removed by R. J. Mathar, Jun 16 2009

More terms from Emeric Deutsch, Jun 14 2009

STATUS

approved

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Last modified April 15 01:24 EDT 2021. Contains 342974 sequences. (Running on oeis4.)