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

Terms

a(0) =1a(1) =3a(2) =1a(3) =1a(4) =4a(5) =8a(6) =22a(7) =55a(8) =145a(9) =386a(10) =1039a(11) =2837a(12) =7808a(13) =21693a(14) =60697a(15) =170959a(16) =484306a(17) =1379020a(18) =3944780a(19) =11330962a(20) =32668988a(21) =94510169a(22) =274262571a(23) =798153211a(24) =2328830794a(25) =6811354123a(26) =19966156857a(27) =58647721275a(28) =172600025350a(29) =508870577560