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 A225602 a(n) = A002426(n^2), where A002426 is the central trinomial coefficients. 2

%I

%S 1,1,19,3139,5196627,82176836301,12159131877715993,

%T 16639279789182494873661,209099036316263774148543463251,

%U 24017537903429183163390175566336055657,25134265191388162956642519120384003897467908119,239089990313305548946878880624659134220897530949847409821

%N a(n) = A002426(n^2), where A002426 is the central trinomial coefficients.

%H G. C. Greubel, <a href="/A225602/b225602.txt">Table of n, a(n) for n = 0..45</a>

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

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

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

%e where exponentiation is an integer series:

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

%t 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 *)

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

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

%Y Cf. A225604, A002426.

%K nonn

%O 0,3

%A _Paul D. Hanna_, Aug 03 2013

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Last modified July 20 11:28 EDT 2019. Contains 325180 sequences. (Running on oeis4.)