a(n) = a(1)*a(n-1) + a(2)*a(n-2) + ... + a(n-1)*a(1) for n >= 4.

Terms

a(0) =1a(1) =1a(2) =0a(3) =1a(4) =2a(5) =6a(6) =16a(7) =45a(8) =126a(9) =358a(10) =1024a(11) =2954a(12) =8580a(13) =25084a(14) =73760a(15) =218045a(16) =647670a(17) =1932230a(18) =5787520a(19) =17398270a(20) =52476700a(21) =158765300a(22) =481690080a(23) =1465239250a(24) =4467799212a(25) =13653601116a(26) =41812009216a(27) =128290240180a(28) =394338641416