A278179 a(n) is the denominator of intersection number , n>=2.

240, 144, 48, 8, 96, 1, 32, 1, 32, 1, 8, 1, 16, 1, 64, 1, 32, 1, 32, 1, 64, 1, 16, 1, 16, 1, 8, 1, 16, 1, 128, 1, 32, 1, 32, 1, 64, 1, 64, 1, 64, 1, 4, 1, 8, 1, 32, 1, 16, 1, 16, 1, 32, 1, 16, 1, 16, 1, 8, 1, 16, 1, 256, 1, 32, 1, 32, 1, 64, 1, 64, 1, 64, 1, 16, 1, 32, 1, 128, 1, 64, 1, 64, 1, 128

Offset: 2

Author

Gheorghe Coserea, Nov 13 2016

Keywords

• nonn
• frac

Comments

For 'intersection numbers' see Section 1 in Itzykson and Zuber paper.

Examples

			7/240, 1225/144, 1816871/48, 7723802625/8, 8591613499103635/96, ...
		

Links

• Gheorghe Coserea, Table of n, a(n) for n = 2..1025
• Stavros Garoufalidis, Marcos Marino, Universality and asymptotics of graph counting problems in nonorientable surfaces, arXiv:0812.1195 [math.CO], 2008.
• C. Itzykson, J.-B. Zuber, Combinatorics of the Modular Group II: the Kontsevich integrals, arXiv:hep-th/9201001, 1991.

Crossrefs

Cf. A269418, A269419, A278178 (numerator).

Programs

PARI

A269418_seq(N) = {
  my(y  = vector(N)); y[1] = 1/48;
  for (n = 2, N,
       y[n] = (25*(n-1)^2-1)/48 * y[n-1] + 1/2*sum(k = 1, n-1, y[k]*y[n-k]));
  concat(-1, y);
};
seq(N) = {
  my(y = A269418_seq(N+2));
  vector(N, g, (3*g)! * 4^(g+1) / ((5*g)*(5*g+2)) * y[g+2]);
};
apply(denominator, seq(85))

Formula

a(n) = denominator((3*n-3)!*4^n/((5*n-5)*(5*n-3)) * A269418(n)/A269419(n)) for n >= 2.