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

A220720

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

Terms

    a(0) =1a(1) =7a(2) =30a(3) =126a(4) =534a(5) =2275a(6) =9667a(7) =41089a(8) =174660a(9) =742428a(10) =3155820a(11) =13414405a(12) =57020437a(13) =242375995a(14) =1030264362a(15) =4379330826a(16) =18615162402a(17) =79127219431a(18) =336345003127

External references