Triangle read by rows: T(n,1) = 1, T(n,k) = T(n-1,k)+(n-1)*T(n-1,k-1) for 1<=k<=n+1.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =2a(6) =1a(7) =4a(8) =6a(9) =6a(10) =1a(11) =7a(12) =18a(13) =24a(14) =24a(15) =1a(16) =11a(17) =46a(18) =96a(19) =120a(20) =120a(21) =1a(22) =16a(23) =101a(24) =326a(25) =600a(26) =720a(27) =720a(28) =1a(29) =22