OFFSET
0,2
COMMENTS
a(n) is the coefficient of t^n in the generating function O(t) = sum_w O_w(t), where w is any binary word on the alphabet {0,1} having as many 0's as 1's.
The series O_w(t) are defined by O_epsilon(t) = 1 (for the empty word epsilon) and O_w(t) = t* sum_{w=aubv} O_u(t)*O_v(t) + t* sum_u O_uw'(t), where: a is a binary letter (0 or 1), b = 1-a, w' is the suffix of w of length |w|-1.
LINKS
Nicolas Bonichon, Mireille Bousquet-Mélou, Paul Dorbec, and Claire Pennarun, On the number of planar Eulerian orientations, HAL preprint <hal-01389264> [math.CO], 2016
Nicolas Bonichon, Mireille Bousquet-Mélou, Paul Dorbec, Claire Pennarun, On the number of planar Eulerian orientations, arXiv:1610.09837 [math.CO], 2016
Claire Pennarun, A C++ program generating the sequence
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Claire Pennarun, Oct 17 2016
STATUS
approved