OFFSET
1,4
COMMENTS
The CWEB program squaregraph.w cited below relates a(n) to the number of certain partitions of {1,2,...,2*n} into n pairs.
REFERENCES
See A194088
LINKS
Don Knuth, squaregraph.w (CWEB program).
EXAMPLE
For n=4 the a(4)=3 cases of perimeter 8 are the two trominoes and the square tetromino.
PROG
(CWEB) (see Knuth link).
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Don Knuth, Aug 15 2011
STATUS
approved