Number of ways to reciprocally link elements of an 2 X n array either to themselves or to exactly one horizontal or antidiagonal neighbor.

A220563

Number of ways to reciprocally link elements of an 2 X n array either to themselves or to exactly one horizontal or antidiagonal neighbor.

Terms

    a(0) =1a(1) =5a(2) =14a(3) =47a(4) =149a(5) =481a(6) =1544a(7) =4965a(8) =15957a(9) =51293a(10) =164870a(11) =529947a(12) =1703417a(13) =5475329a(14) =17599456a(15) =56570281a(16) =181834969a(17) =584475733a(18) =1878691886a(19) =6038716423a(20) =19410365421a(21) =62391120801a(22) =200545011400a(23) =644615789581

External references