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A360047
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a(n) = Sum_{k=0..floor(n/5)} binomial(n+4,5*k+4) * Catalan(k).
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4
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1, 5, 15, 35, 70, 127, 220, 385, 715, 1430, 3005, 6400, 13500, 28050, 57800, 119515, 250425, 533525, 1151975, 2504700, 5453176, 11856275, 25748450, 55962300, 121981725, 266968938, 586630515, 1292992795, 2855288480, 6311930460, 13963767356, 30919563310
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OFFSET
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0,2
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LINKS
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FORMULA
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a(n) = binomial(n+4,4) + Sum_{k=0..n-5} a(k) * a(n-k-5).
G.f. A(x) satisfies: A(x) = 1/(1-x)^5 + x^5 * A(x)^2.
G.f.: 2 / ( (1-x)^2 * ((1-x)^3 + sqrt((1-x)^6 - 4*x^5*(1-x))) ).
D-finite with recurrence (n+5)*a(n) +6*(-n-4)*a(n-1) +15*(n+3)*a(n-2) +20*(-n-2)*a(n-3) +15*(n+1)*a(n-4) +10*(-n+1)*a(n-5) +5*(n-1)*a(n-6)=0. - R. J. Mathar, Jan 25 2023
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PROG
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(PARI) a(n) = sum(k=0, n\5, binomial(n+4, 5*k+4)*binomial(2*k, k)/(k+1));
(PARI) my(N=40, x='x+O('x^N)); Vec(2/((1-x)^2*((1-x)^3+sqrt((1-x)^6-4*x^5*(1-x)))))
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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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