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A278121 a(n) is denominator of rational z(n) associated with the non-orientable map asymptotics constant p((n+1)/2). 2
1, 12, 144, 864, 27648, 248832, 11943936, 35831808, 1528823808, 1719926784, 220150628352, 2972033482752, 1141260857376768, 106993205379072, 54780521154084864, 13695130288521216, 42071440246337175552, 739537035580145664, 6058287395472553279488 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Gheorghe Coserea, Table of n, a(n) for n = 0..201

S. R. Carrell, The Non-Orientable Map Asymptotics Constant pg, arXiv:1406.1760 [math.CO], 2014.

Stavros Garoufalidis, Marcos Marino, Universality and asymptotics of graph counting problems in nonorientable surfaces, arXiv:0812.1195 [math.CO], 2008.

FORMULA

a(n) = denominator(z(n)), where z(n) = 1/2 * (y(n/2)/3^(n/2) + (5*n-6)/6 * z(n-1) + Sum {k=1..n-1} z(k)*z(n-k)), with z(0) = -1, y(n) = A269418(n)/A269419(n) and y(n+1/2) = 0 for all n.

p((n+1)/2) = 4 * (A278120(n)/A278121(n)) * (3/2)^((n+1)/2) / gamma((5*n-1)/4), where p((n+1)/2) is the non-orientable map asymptotics constant for type g=(n+1)/2 and gamma is the Gamma function.

EXAMPLE

For n=3 we have p(2) = 4 * (25/864) * (3/2)^2 / gamma(7/2) = 5/(36*sqrt(Pi)).

For n=5 we have p(3) = 4 * (15745/248832)*(3/2)^3/gamma(6) = 3149/442368.

n   z(n)                   p((n+1)/2)

0   -1                     3/(sqrt(6)*gamma(3/4))

1   1/12                   1/2

2   5/144                  2/(sqrt(6)*gamma(1/4))

3   25/864                 5/(36*sqrt(Pi))

4   1033/27684             1033/(13860*sqrt(6)*gamma(3/4))

5   15745/248832           3149/442368

6   1599895/11943936       319979/(18796050*sqrt(6)*gamma(1/4))

7   12116675/35831808      484667/(560431872*sqrt(Pi))

8   1519810267/1528823808  1519810267/(4258429005600*sqrt(6)*gamma(3/4))

9   5730215335/1719926784  1146043067/41094783959040

...

PROG

(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), z = vector(N)); z[1] = 1/12;

  for (n = 2, N,

       my(t1 = if(n%2, 0, y[1+n\2]/3^(n\2)),

          t2 = sum(k=1, n-1, z[k]*z[n-k]));

      z[n] = (t1 + (5*n-6)/6 * z[n-1] + t2)/2);

  concat(-1, z);

};

apply(denominator, seq(18))

CROSSREFS

Cf. A269418, A269419, A278120 (numerator).

Sequence in context: A206937 A188602 A188690 * A188609 A206873 A188846

Adjacent sequences:  A278118 A278119 A278120 * A278122 A278123 A278124

KEYWORD

nonn,frac

AUTHOR

Gheorghe Coserea, Nov 12 2016

STATUS

approved

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Last modified September 30 17:27 EDT 2022. Contains 357106 sequences. (Running on oeis4.)