A binomial convolution recurrence sequence.

Terms

a(0) =0a(1) =0a(2) =1a(3) =1a(4) =2a(5) =6a(6) =18a(7) =54a(8) =173a(9) =605a(10) =2274a(11) =9020a(12) =37486a(13) =163128a(14) =743101a(15) =3535765a(16) =17518018a(17) =90126158a(18) =480514430a(19) =2650912738a(20) =15112253425a(21) =88903779401a(22) =539003066674