OFFSET
0,3
LINKS
S. N. Perepechko, Number of perfect matchings on triangular lattices of fixed width, DIMA'2015 slides.
FORMULA
G.f.: (1-z)*(1+z)*(1-z-5*z^2-z^3+z^4)/((1+z-3*z^2-3*z^3+z^4)*(1-3*z-3*z^2+z^3+z^4)).
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Sergey Perepechko, Jul 13 2019
STATUS
approved