Number of ways to reciprocally link elements of an 3Xn array either to themselves or to exactly two horizontal, diagonal or antidiagonal neighbors.

A220727

Number of ways to reciprocally link elements of an 3Xn array either to themselves or to exactly two horizontal, diagonal or antidiagonal neighbors.

Terms

    a(0) =1a(1) =4a(2) =30a(3) =230a(4) =1819a(5) =14466a(6) =114900a(7) =913187a(8) =7256380a(9) =57664692a(10) =458236178a(11) =3641435760a(12) =28937067889a(13) =229951848995

External references