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Number of lattice paths from (0,0) to (n,n) using steps S={(k,0),(0,k),(r,r)|0<k<=2,0<r<=2} which never go above the line y=x.
4

%I #7 Mar 30 2012 19:01:01

%S 1,2,10,55,351,2401,17248,128221,978082,7612155,60204488,482481220,

%T 3909460725,31974923487,263623879118,2188682538746,18282238300443,

%U 153537981720402,1295640515428649,10980400434511117,93418283866708579

%N Number of lattice paths from (0,0) to (n,n) using steps S={(k,0),(0,k),(r,r)|0<k<=2,0<r<=2} which never go above the line y=x.

%Y Cf. A175934, A175936, A175937, A175939

%K nonn

%O 0,2

%A _Eric Werley_, Dec 06 2010