Permanent of the n-th principal submatrix of A204269.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =6a(5) =20a(6) =48a(7) =288a(8) =1344a(9) =6624a(10) =28512a(11) =212544a(12) =1425600a(13) =10056960a(14) =61378560a(15) =600514560a(16) =5185658880a(17) =46664294400a(18) =374492160000