Permanent of the n-th principal submatrix of A204439.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =6a(5) =20a(6) =80a(7) =384a(8) =2016a(9) =12096a(10) =82080a(11) =597888a(12) =4783104a(13) =41886720a(14) =389145600a(15) =3891456000a(16) =41803776000a(17) =472283136000