Number of permutations p of [2*n] satisfying Sum_{i=1..2*n} (p(i)-i)^2 = 2*n.
A391664
Number of permutations p of [2*n] satisfying Sum_{i=1..2*n} (p(i)-i)^2 = 2*n.
Terms
- a(0) =1a(1) =1a(2) =1a(3) =9a(4) =47a(5) =177a(6) =691a(7) =3001a(8) =13274a(9) =57912a(10) =252497a(11) =1109961a(12) =4908590a(13) =21763925a(14) =96687202a(15) =430528955a(16) =1921312439a(17) =8589901368a(18) =38463789496a(19) =172476073461a(20) =774406324182
External references
- oeis: A391664