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A209331
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a(n) = Sum_{k=0..[n/2]} binomial((n-k)^2, n*k-k^2).
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6
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1, 1, 2, 7, 86, 1905, 66002, 5218373, 1340847046, 688750226335, 527838995308056, 707409447204872377, 2844096719471817175298, 30274246332924074325724393, 517646331335208169889265781259, 13363896516779950029547538703868509
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OFFSET
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0,3
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LINKS
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FORMULA
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Equals the antidiagonal sums of triangle A209330(n,k) = C(n^2,n*k).
Limit n->infinity a(n)^(1/n^2) = ((1-r)/r)^((1-r)^2/(3-4*r)) = 1.4360944969025357119535113523184471047971386419..., where r = A323777 = 0.220676041323740696312822269998050167187681031... is the root of the equation (1-2*r)^(3-4*r) = (1-r)^(2-2*r) * r^(1-2*r). - Vaclav Kotesovec, Mar 03 2014
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MATHEMATICA
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Table[Sum[Binomial[(n-k)^2, n*k-k^2], {k, 0, Floor[n/2]}], {n, 0, 20}] (* Vaclav Kotesovec, Mar 03 2014 *)
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PROG
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(PARI) {a(n)=sum(k=0, n\2, binomial((n-k)^2, n*k-k^2))}
for(n=0, 20, print1(a(n), ", "))
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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