Meandric numbers for a river crossing up to 14 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) =1152a(10) =3452a(11) =9158a(12) =28178a(13) =76539a(14) =240370a(15) =665128a(16) =2123437a(17) =5964658a(18) =19302248a(19) =54897742a(20) =179695133a(21) =516457890a(22) =1707112980a(23) =4950547189a(24) =16502992754a(25) =48230509790a(26) =161979310981a(27) =476609746441