OFFSET
1,1
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..30
S. Butler and S. Osborne, Counting tilings by taking walks, 2012.
FORMULA
Empirical g.f.: -x * (3*x^7 - 5*x^6 - 33*x^5 + 27*x^4 + 61*x^3 + 45*x^2 - 15*x - 3) / ( (x + 1) * (x^2 - 4*x + 1) * (x^2 - 2*x - 1) * (x^2 + 2*x - 1) ). - Joerg Arndt, Nov 17 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Dec 27 2012
EXTENSIONS
a(1)-a(2),a(11)-a(20) from Andrew Howroyd, Nov 15 2015
STATUS
approved