Number of planar lattice convex polygonal lines joining the origin and the point (n,n).

Terms

a(0) =1a(1) =2a(2) =5a(3) =13a(4) =32a(5) =77a(6) =178a(7) =399a(8) =877a(9) =1882a(10) =3959a(11) =8179a(12) =16636a(13) =33333a(14) =65894a(15) =128633a(16) =248169a(17) =473585a(18) =894573a(19) =1673704a(20) =3103334a(21) =5705383a(22) =10405080a(23) =18831761a(24) =33836627a(25) =60378964a(26) =107035022a(27) =188553965a(28) =330166814a(29) =574815804