Number of ways to reciprocally link elements of an 3 X n array either to themselves or to exactly two horizontal or antidiagonal neighbors.

A220633

Number of ways to reciprocally link elements of an 3 X n array either to themselves or to exactly two horizontal or antidiagonal neighbors.

Terms

    a(0) =1a(1) =1a(2) =3a(3) =12a(4) =44a(5) =158a(6) =564a(7) =2010a(8) =7160a(9) =25502a(10) =90828a(11) =323490a(12) =1152128a(13) =4103366a(14) =14614356a(15) =52049802a(16) =185378120a(17) =660233966a(18) =2351458140a(19) =8374842354a(20) =29827443344a(21) =106232014742a(22) =378350930916

External references