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A269419
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a(n) is denominator of y(n), where y(n+1) = (25*n^2-1)/48 * y(n) + (1/2)*Sum_{k=1..n}y(k)*y(n+1-k), with y(0) = -1.
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9
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1, 48, 4608, 55296, 42467328, 84934656, 21743271936, 36691771392, 400771988324352, 1352605460594688, 16620815899787526144, 779100745302540288, 153177439332441840943104, 2393397489569403764736, 235280546814630667688607744, 57441539749665690353664
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OFFSET
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0,2
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LINKS
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Edward A. Bender, Zhicheng Gao, L. Bruce Richmond, The map asymptotics constant tg, The Electronic Journal of Combinatorics, Volume 15 (2008), Research Paper #R51.
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FORMULA
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t(g) = (A269418(g)/A269419(g)) / (2^(g-2) * gamma((5*g-1)/2)), where t(g) is the orientable map asymptotics constant and gamma is the Gamma function.
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EXAMPLE
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For n=0 we have t(0) = (-1) / (2^(-2)*gamma(-1/2)) = 2/sqrt(Pi).
For n=1 we have t(1) = (1/48) / (2^(-1)*gamma(2)) = 1/24.
n y(n) t(n)
0 -1 2/sqrt(Pi)
1 1/48 1/24
2 49/4608 7/(4320*sqrt(Pi))
3 1225/55296 245/15925248
4 4412401/42467328 37079/(96074035200*sqrt(Pi))
5 73560025/84934656 38213/14089640214528
6 245229441961/21743271936 5004682489/(92499927372103680000*sqrt(Pi))
7 7759635184525/36691771392 6334396069/20054053184087387013120
...
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MATHEMATICA
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y[0] = -1;
y[n_] := y[n] = (25(n-1)^2-1)/48 y[n-1] + 1/2 Sum[y[k] y[n-k], {k, 1, n-1}];
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PROG
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(PARI)
seq(n) = {
my(y = vector(n));
y[1] = 1/48;
for (g = 1, n-1,
y[g+1] = (25*g^2-1)/48 * y[g] + 1/2*sum(k = 1, g, y[k]*y[g+1-k]));
return(concat(-1, y));
}
apply(denominator, seq(14))
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CROSSREFS
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KEYWORD
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nonn,frac
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AUTHOR
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STATUS
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approved
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