login
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
OFFSET
0,2
LINKS
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
KEYWORD
nonn,frac
AUTHOR
Gheorghe Coserea, Nov 12 2016
STATUS
approved