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A336945
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a(n) = binomial(3*n,n)/(2*n + 1) - 2*binomial(3*(n - 1),n - 1)/(2*n - 1) for n > 0 with a(0) = 1.
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0
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1, -1, 1, 6, 31, 163, 882, 4896, 27759, 160149, 937365, 5553210, 33237828, 200696356, 1221105376, 7479222624, 46079243631, 285373035417, 1775569951995, 11093660204970, 69574265317095, 437832231422355, 2763889941603630, 17497374053053440, 111061430519553540, 706647507156148428, 4506221447451530172
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OFFSET
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0,4
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LINKS
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FORMULA
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O.g.f.: (1 - 2*z)*2*sin(arcsin(sqrt(27*z)/2)/3)/sqrt(3*z). [This is due to Emeric Deutsch.]
D-finite with recurrence 2*n*(2*n+1)*a(n) +(-43*n^2+67*n-18)*a(n-1) +4*(31*n^2-130*n+117)*a(n-2) -12*(3*n-10)*(3*n-11)*a(n-3)=0. - R. J. Mathar, Mar 06 2022
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MAPLE
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# Recurrence:
a := proc(n) option remember; if n < 4 then return [1, -1, 1, 6][n+1] fi;
-((-108*n^2 + 756*n - 1320)*a(n - 3) + (124*n^2 - 520*n + 468)*a(n - 2) + (-43*n^2 + 67*n - 18)*a(n - 1)) / (4*n^2 + 2*n) end:
alias(PS=ListTools:-PartialSums): A336945List := proc(m) local A, P, n;
A := [1, -1, 1]; P := [1, 1]; for n from 1 to m - 2 do P := PS(PS([op(P), P[-1]]));
A := [op(A), P[-1]] od; A end: A336945List(26); # Peter Luschny, Mar 26 2022
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MATHEMATICA
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a[n_] := Binomial[3*n, n]/(2*n + 1) - 2 * Binomial[3*(n - 1), n - 1]/(2*n - 1); Array[a, 27, 0] (* Amiram Eldar, Aug 08 2020 *)
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PROG
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(PARI) a(n) = if (n!=0, binomial(3*n, n)/(2*n + 1) - 2*binomial(3*(n - 1), n - 1)/(2*n - 1), 1); \\ Michel Marcus, Aug 09 2020
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CROSSREFS
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KEYWORD
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sign
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AUTHOR
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STATUS
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approved
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