%I #7 Mar 30 2012 19:01:01
%S 1,2,9,50,314,2116,14949,109246,818978,6263072,48668366,383182648,
%T 3050196328,24506969724,198482172753,1618700191002,13281652367078,
%U 109564878995724,908171084052990,7560049450347964,63176859344766204
%N Number of lattice paths from (0,0) to (n,n) using steps S={(k,0),(0,k),(1,1)|0<k<=2} which never go above the line y=x.
%e a(2)=9 because we can reach (2,2) in the following ways:
%e (1,0),(1,0),(0,1),(0,1)
%e (1,0),(1,0),(0,2)
%e (2,0),(0,1),(0,1)
%e (2,0),(0,2)
%e (1,0),(1,1),(0,1)
%e (1,0),(0,1),(1,1)
%e (1,1),(1,0),(0,1)
%e (1,1),(0,1),(1,0)
%e (1,1)(1,1)
%Y Cf. A006318
%K nonn
%O 0,2
%A _Eric Werley_, Dec 05 2010