OFFSET
1,1
COMMENTS
Upper bounded by 3^{n*(n+1)}.
LINKS
John Tromp, Table of n, a(n) for n = 1..19
John Tromp, Number of legal Go positions
J. Tromp and G. Farnebäck, Combinatorics of Go, Lecture Notes in Computer Science, 4630, 84-99, 2007.
EXAMPLE
For n=1 the 5 legal 1x2 boards are .. X. O. .X .O
CROSSREFS
KEYWORD
nonn,hard
AUTHOR
John Tromp, Jan 26 2016
STATUS
approved