OFFSET
0,3
EXAMPLE
For n=4 the paths UUUDDUDD and UUDUUDDD fail the definition because {2,2} != {3,1} so a(4) = 12 rather than Catalan(4)=14.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
David Scambler, Jan 08 2011
EXTENSIONS
a(15)-a(18) from Alois P. Heinz, May 07 2012
STATUS
approved