OFFSET
4,2
COMMENTS
By empirical evidence, the terms possess a curious prime factor behavior. E.g. 2^4*3^4*5^2*7*11*13^2 divides a(16)=11024455369912310561835600.
LINKS
A. Gagarin et al., Table of n, a(n) for n = 4..20
A. Gagarin, G. Labelle and P. Leroux, Counting labeled projective-planar graphs without a K_{3,3}-subdivision, arXiv:math/0406140 [math.CO], 2004-2006.
CROSSREFS
KEYWORD
nonn
AUTHOR
Valery A. Liskovets, Mar 22 2005
STATUS
approved