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A277924
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a(n) = Sum_{i=0..n+1} binomial(2*n,n-i+1).
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1
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1, 4, 15, 57, 219, 848, 3302, 12911, 50643, 199140, 784626, 3096514, 12236830, 48412432, 191718188, 759852347, 3013746563, 11960699132, 47494802618, 188689585982, 749961486698, 2981943800192, 11860758904148, 47191458566582
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OFFSET
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0,2
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COMMENTS
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LINKS
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FORMULA
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G.f.: x^2*(1 - 2*x - sqrt(1 - 4*x))/(sqrt(1 - 4*x)*(4*x^3 - 13*x^2 + 7*x - 1) - 20*x^3 + 25*x^2 - 9*x + 1) - 1/x = (-1 + 5*x + (1 - x)*sqrt(1 - 4*x))/(2*x*(1 - 4*x)).
a(n) = 2^(2*n-1) - 4^n*(n-1/2)!/(sqrt(Pi)*(n+1)!) + 3*2^(2*n-1)*(n-1/2)!/(sqrt(Pi)*n!). - Bruno Berselli, Nov 04 2016
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MAPLE
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a:= proc(n) option remember; `if`(n<3,
[1, 4, 15][n+1], ((2*(4*n^2-7*n-1))*a(n-1)
-(8*(n-1))*(2*n-3)*a(n-2))/((n-2)*(n+1)))
end:
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MATHEMATICA
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Table[((3n + 1) CatalanNumber[n] + 4^n)/2, {n, 0, 23}] (* Peter Luschny, Nov 04 2016 *)
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PROG
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(Maxima) makelist(sum(binomial(2*n, n-i+1), i, 0, n+1), n, 0, 30);
(PARI) a(n) = sum(k=0, n+1, binomial(2*n, n-k+1)); \\ Michel Marcus, Nov 04 2016
(Sage)
def a():
c, f, b, n = 1, 1, 1, 1
while True:
yield (c*f + b)//2
c = (4*n - 2)*c//(n + 1)
b <<= 2
f += 3
n += 1
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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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