a(n) = floor(n^n/n!!).

Terms

a(0) =1a(1) =2a(2) =9a(3) =32a(4) =208a(5) =972a(6) =7843a(7) =43690a(8) =409968a(9) =2604166a(10) =27447010a(11) =193491763a(12) =2241278030a(13) =17224712961a(14) =216027868615