Number of paths in the plane x >= 0 and y >= -2, from (0,0) to (n,0), and consisting of steps U = (1,1), D = (1,-1) and H = (1,0).

A026325

Number of paths in the plane x >= 0 and y >= -2, from (0,0) to (n,0), and consisting of steps U = (1,1), D = (1,-1) and H = (1,0).

Terms

    a(0) =1a(1) =1a(2) =3a(3) =7a(4) =19a(5) =51a(6) =140a(7) =386a(8) =1071a(9) =2983a(10) =8338a(11) =23376a(12) =65715a(13) =185199a(14) =523134a(15) =1480872a(16) =4200411a(17) =11936619a(18) =33981063a(19) =96897759a(20) =276739029a(21) =791532973a(22) =2267119660a(23) =6502108902a(24) =18671460905a(25) =53680763201a(26) =154507444731a(27) =445190930863

External references