Number of ways to reciprocally link elements of a 2 X n array either to themselves or to exactly two horizontal, diagonal or antidiagonal neighbors.

A220726

Number of ways to reciprocally link elements of a 2 X n array either to themselves or to exactly two horizontal, diagonal or antidiagonal neighbors.

Terms

    a(0) =1a(1) =2a(2) =7a(3) =21a(4) =68a(5) =221a(6) =717a(7) =2330a(8) =7571a(9) =24601a(10) =79940a(11) =259761a(12) =844081a(13) =2742802a(14) =8912607a(15) =28961101a(16) =94107748a(17) =305798741a(18) =993678757a(19) =3228912810a(20) =10492201691a(21) =34093920401a(22) =110786605380a(23) =359995910921

External references