Permanent of the n-th principal submatrix of A204549.

Terms

a(0) =0a(1) =1a(2) =1a(3) =2a(4) =4a(5) =20a(6) =72a(7) =288a(8) =864a(9) =6624a(10) =35424a(11) =212544a(12) =1088640a(13) =10056960a(14) =75064320a(15) =600514560a(16) =4147200000a(17) =46664294400a(18) =440681472000