Central numbers in the (2,3)-Pascal triangle A029600.

Terms

a(0) =1a(1) =5a(2) =15a(3) =50a(4) =175a(5) =630a(6) =2310a(7) =8580a(8) =32175a(9) =121550a(10) =461890a(11) =1763580a(12) =6760390a(13) =26001500a(14) =100291500a(15) =387793800a(16) =1502700975a(17) =5834015550a(18) =22687838250a(19) =88363159500a(20) =344616322050