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A352626
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a(n) = (n+1)*(3*n-2)*C(2*n,n-1)/(4*n-2).
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1
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1, 8, 42, 200, 910, 4032, 17556, 75504, 321750, 1361360, 5727436, 23984688, 100053772, 416024000, 1725013800, 7135405920, 29452939110, 121347523440, 499132441500, 2050025300400, 8408638258020, 34448503964160, 140974630569240, 576340150932000, 2354075068866300
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OFFSET
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1,2
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COMMENTS
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This is half the number of edges of the origami flip graph of the all-equal-angle single-vertex crease pattern of degree 2n.
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LINKS
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FORMULA
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G.f.: x*(2*x+1)/(1-4*x)^(3/2).
D-finite with recurrence (-n+1)*a(n) +2*(n+2)*a(n-1) +4*(2*n-5)*a(n-2)=0. - R. J. Mathar, Mar 29 2022
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MAPLE
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a:=n->(n+1)*(3*n-2)*binomial(2*n, n-1)/(4*n-2):
seq(a(n), n=1..33);
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MATHEMATICA
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a[n_] := (n + 1)*(3*n - 2)*Binomial[2*n, n - 1]/(4*n - 2); Array[a, 25] (* Amiram Eldar, Mar 25 2022 *)
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PROG
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(PARI) a(n) = (n+1)*(3*n-2)*binomial(2*n, n-1)/(4*n-2); \\ Michel Marcus, Mar 25 2022
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CROSSREFS
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Number of vertices of the origami flip graph of the all-equal-angle single-vertex crease pattern of degree 2n is A162551.
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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