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A361752
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a(n) = Sum_{k=0..floor(n/2)} binomial(2*(n-2*k),k) * binomial(2*(n-2*k),n-2*k).
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2
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1, 2, 6, 24, 94, 374, 1520, 6252, 25942, 108408, 455586, 1923444, 8151856, 34661252, 147788484, 631660788, 2705471254, 11609393084, 49899207640, 214792704256, 925811868178, 3995288307392, 17260287754284, 74641620619072, 323080683587056, 1399606566298916
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OFFSET
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0,2
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COMMENTS
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Diagonal of rational function 1/(1 - (1 + (x*y)^2) * (x + y)).
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LINKS
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FORMULA
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G.f.: 1/sqrt(1 - 4*x*(1 + x^2)^2).
n*a(n) = 2*(2*n-1)*a(n-1) + 4*(2*n-3)*a(n-3) + 2*(2*n-5)*a(n-5) for n > 4.
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PROG
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(PARI) a(n) = sum(k=0, n\2, binomial(2*(n-2*k), k)*binomial(2*(n-2*k), n-2*k));
(Python)
from math import comb
def A361752(n): return sum(comb(m:=(r:=n-(k<<1))<<1, k)*comb(m, r) for k in range((n>>1)+1)) # Chai Wah Wu, Mar 23 2023
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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