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A225602 a(n) = A002426(n^2), where A002426 is the central trinomial coefficients. 2
1, 1, 19, 3139, 5196627, 82176836301, 12159131877715993, 16639279789182494873661, 209099036316263774148543463251, 24017537903429183163390175566336055657, 25134265191388162956642519120384003897467908119, 239089990313305548946878880624659134220897530949847409821 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..45

FORMULA

Logarithmic derivative of A225604 (ignoring the initial term of this sequence).

a(n) = Sum_{k=0..floor(n^2/2)} binomial(n^2, k) * binomial(n^2-k, k).

EXAMPLE

L.g.f.: L(x) = x + 19*x^2/2 + 3139*x^3/3 + 5196627*x^4/4 + 82176836301*x^5/5 + ...

where exponentiation is an integer series:

exp(L(x)) = 1 + x + 10*x^2 + 1056*x^3 + 1300253*x^4 + 16436676927*x^5 + ... + A225604(n)*x^n + ...

MATHEMATICA

Table[Sum[Binomial[n^2, k]*Binomial[n^2 - k, k], {k, 0, Floor[n^2/2]}], {n, 0, 50}] (* G. C. Greubel, Feb 27 2017 *)

PROG

(PARI) {a(n)=sum(k=0, n^2\2, binomial(n^2, k)*binomial(n^2-k, k))}

for(n=0, 20, print1(a(n), ", "))

CROSSREFS

Cf. A225604, A002426.

Sequence in context: A196541 A221296 A287938 * A195756 A125197 A238563

Adjacent sequences:  A225599 A225600 A225601 * A225603 A225604 A225605

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Aug 03 2013

STATUS

approved

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Last modified June 25 17:47 EDT 2019. Contains 324353 sequences. (Running on oeis4.)