a(n) = a(1)*a(n-1) + a(2)*a(n-2) + ... + a(n-3)*a(3) for n >= 4, with initial terms 1, 1, 2, 2.

Terms

a(0) =1a(1) =1a(2) =2a(3) =2a(4) =4a(5) =10a(6) =22a(7) =52a(8) =130a(9) =326a(10) =832a(11) =2162a(12) =5674a(13) =15032a(14) =40178a(15) =108154a(16) =292956a(17) =797994a(18) =2184430a(19) =6006028a(20) =16579138a(21) =45929838a(22) =127656504a(23) =355863330a(24) =994735442a(25) =2787537904a(26) =7829586914a(27) =22038759218a(28) =62158281844a(29) =175636481738