Number of permutations p of {1,2,3,...,n} such that Sum_{k=1..n} abs(k-p(k)) = 2n.

A072949

Number of permutations p of {1,2,3,...,n} such that Sum_{k=1..n} abs(k-p(k)) = 2n.

Terms

    a(0) =1a(1) =0a(2) =0a(3) =0a(4) =4a(5) =24a(6) =148a(7) =744a(8) =3696a(9) =17640a(10) =83420a(11) =390144a(12) =1817652a(13) =8438664a(14) =39117852a(15) =181136304a(16) =838372452a(17) =3879505944a(18) =17952463180a(19) =83086702848a(20) =384626048292

External references