Number of ways to reciprocally link elements of an n X 2 array either to themselves or to exactly two king-move neighbors, without 3-loops.

A220647

Number of ways to reciprocally link elements of an n X 2 array either to themselves or to exactly two king-move neighbors, without 3-loops.

Terms

    a(0) =1a(1) =4a(2) =23a(3) =83a(4) =344a(5) =1441a(6) =5881a(7) =24220a(8) =99767a(9) =410363a(10) =1688864a(11) =6950497a(12) =28602385a(13) =117707380a(14) =484400087a(15) =1993438499a(16) =8203560488a(17) =33759953377a(18) =138931649065a(19) =571742660236

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