Number of permutations of 2 copies of 1..n avoiding adjacent step pattern up, down.

A177554

Number of permutations of 2 copies of 1..n avoiding adjacent step pattern up, down.

Terms

    a(0) =1a(1) =4a(2) =28a(3) =304a(4) =4576a(5) =91072a(6) =2306176a(7) =71993344a(8) =2707268608a(9) =120392433664

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