Nearest integer to 2*n!*(2/Pi)^(n+1).

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =5a(5) =16a(6) =61a(7) =272a(8) =1385a(9) =7936a(10) =50521a(11) =353791a(12) =2702767a(13) =22368251a(14) =199360995a(15) =1903757268a(16) =19391512295a(17) =209865342434