Series expansion for rectilinear polymers on square lattice.

Terms

a(0) =7a(1) =63a(2) =254a(3) =710a(4) =1605a(5) =3157a(6) =5628a(7) =9324a(8) =14595a(9) =21835a(10) =31482a(11) =44018a(12) =59969a(13) =79905a(14) =104440a(15) =134232a(16) =169983a(17) =212439a(18) =262390a(19) =320670a(20) =388157a(21) =465773a(22) =554484a(23) =655300a(24) =769275a(25) =897507a(26) =1041138a(27) =1201354a(28) =1379385