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A303865
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Number of noncrossing path sets on 3*n nodes up to rotation with each path having exactly 3 nodes.
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4
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1, 1, 6, 38, 384, 4425, 57976, 807318, 11828706, 179826245, 2816100678, 45170552490, 739103543356, 12297976924176, 207577047945312, 3547290764931730, 61277684496311364, 1068648890500799799, 18794421104465407618, 333037302131948734566, 5941487005826379359448
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OFFSET
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0,3
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LINKS
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FORMULA
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a(n) ~ 3^(4*n - 1/2) / (sqrt(Pi) * n^(5/2) * 2^(2*n + 2)). - Vaclav Kotesovec, Jun 01 2022
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MATHEMATICA
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seq[n_] := Module[{p, q}, p = 1 + InverseSeries[x/(3*(1 + x)^3) + O[x]^n]; q = x*D[p, x]/p; Integrate[((p - 1)/3 + Sum[EulerPhi[d]*(q /. x -> x^d + O[x]^n), {d, 2, n}])/x, x] + 1];
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PROG
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(PARI)
seq(n)={ my(p=1 + serreverse( x/(3*(1 + x)^3) + O(x*x^n) )); my(q=x*deriv(p)/p);
Vec(intformal(((p-1)/3 + sum(d=2, n, eulerphi(d)*subst(q, x, x^d+O(x*x^n))))/x) + 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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