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A036914 a(n) = C(2*n,n)*C(3*n,2*n)^4. 0
1, 162, 303750, 995742720, 4202607543750, 20493770553668412, 109738295483524291584, 627433021349790289920000, 3765656995768668039930646470, 23460102529588600192836492187500, 150552597141762184641565143623272500, 989711604190467147276644388444241920000 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

REFERENCES

The right-hand side of a binomial coefficient identity in H. W. Gould, Combinatorial Identities, Morgantown, 1972; Eq 21.1 page 72 (see the Formula section).

From Peter Bala, Aug 07 2016: (Start)

Compare with the identities:

Sum_{k = 0..2*n} (-1)^(n+k)*binomial(3*n,k)^2*binomial(3*n - k,n)^2 = binomial(3n,n)^2*binomial(2*n,n) = A275047(n), and

Sum_{k = 0..2*n} (-1)^k*binomial(3*n,k)*binomial(3*n - k,n)^3 = binomial(3*n,n)*binomial(2*n,n) = (3*n)!/n!^3 = A006480(n). (Sprugnoli, Section 2.9, Table 10, p. 123).

Sum_{k = 0..2*n} (-1)^k*binomial(2*n,k)*binomial(3*n - k,n)^2 = A000984(n). (End)

LINKS

Table of n, a(n) for n=0..11.

R. Sprugnoli, Riordan array proofs of identities in Gould's book

FORMULA

Sum_{k=0..2*n} (-1)^k*C(3*n, k)^3*C(3*n-k, n)^3 = (-1)^n*C(2*n, n)*C(3*n, 2*n)^4.

From Peter Bala, Aug 07 2016: (Start)

a(n) = (3*n)!^4/(n!^6*(2*n)!^3).

a(n) = A005809(n)^4 * A000984(n) = A005809(n)^3 * A006480(n) = A005809(n)^2 * A275047(n).

a(n) = {[x^n] (1 + x)^(3*n)}^4 * [x^n] (1 + x)^(2*n) = [x^n] G(x)^(162*n), where G(x) = 1 + x + 776*x^2 + 1633370*x^3 + 5060509158*x^4 + 19379170742458*x^5 + 84908023350007787*x^6 + ... appears to have integer coefficients.

exp( Sum_{n >= 1} a(n)*x^n/n ) = F(x)^162, where F(x) = 1 + x + 938*x^2 + 2049791*x^3 + 6487994244*x^4 + 25309359070330*x^5 + 112932966264239483*x^6 + ... appears to have integer coefficients. (End)

a(n) ~ (9/16)*9^(6*n)/((Pi*n)^(5/2)*64^n). - Ilya Gutkovskiy, Aug 07 2016

MAPLE

seq((3*n)!^4/(n!^6*(2*n)!^3), n = 0..20); # Peter Bala, Aug 07 2016

MATHEMATICA

Table[Binomial[2 n, n] Binomial[3 n, 2 n]^4, {n, 0, 11}] (* Michael De Vlieger, Aug 07 2016 *)

CROSSREFS

Cf. A000984, A005809, A006480, A275047.

Sequence in context: A209965 A230837 A183812 * A214185 A214236 A030442

Adjacent sequences:  A036911 A036912 A036913 * A036915 A036916 A036917

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane.

STATUS

approved

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Last modified September 25 09:30 EDT 2016. Contains 276529 sequences.