a(n) = a(n-1) - a(n-2) + a(n-3) + a(n-4), with a(1) = a(2) = a(3) = a(4) = 1.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =3a(6) =3a(7) =3a(8) =5a(9) =8a(10) =9a(11) =9a(12) =13a(13) =21a(14) =26a(15) =27a(16) =35a(17) =55a(18) =73a(19) =80a(20) =97a(21) =145a(22) =201a(23) =233a(24) =274a(25) =387a(26) =547a(27) =667a(28) =781a(29) =1048