Number of nonisomorphic ways a loop can cross two parallel roads 2n times.

A086031

Number of nonisomorphic ways a loop can cross two parallel roads 2n times.

Terms

    a(0) =1a(1) =1a(2) =3a(3) =7a(4) =37a(5) =207a(6) =1470a(7) =11169a(8) =91166a(9) =776841a(10) =6865598a(11) =62443973

External references