a(n) = a(1)*a(n-1) + a(2)*a(n-2) + ... + a(n-1)*a(1) for n >= 3.

Terms

a(0) =0a(1) =1a(2) =2a(3) =4a(4) =12a(5) =40a(6) =144a(7) =544a(8) =2128a(9) =8544a(10) =35008a(11) =145792a(12) =615296a(13) =2625792a(14) =11311616a(15) =49124352a(16) =214838528a(17) =945350144a(18) =4182412288a(19) =18593224704a(20) =83015133184a(21) =372090122240