Meandric numbers for a river crossing up to 8 parallel roads at n points.

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =10a(5) =23a(6) =63a(7) =155a(8) =448a(9) =1151a(10) =3450a(11) =9137a(12) =28134a(13) =76236a(14) =239712a(15) =661374a(16) =2115046a(17) =5921549a(18) =19203568a(19) =54422726a(20) =178585838a(21) =511343777a(22) =1694965469a(23) =4896195579a(24) =16371992897a(25) =47656781437a(26) =160578870274a(27) =470571482142