a(n) = 3*a(n-1) - 4*a(n-2) + 6*a(n-3) - 4*a(n-4), with initial terms 1,2,4,7.

Terms

a(0) =1a(1) =2a(2) =4a(3) =7a(4) =13a(5) =27a(6) =55a(7) =107a(8) =211a(9) =427a(10) =859a(11) =1707a(12) =3403a(13) =6827a(14) =13675a(15) =27307a(16) =54571a(17) =109227a(18) =218539a(19) =436907a(20) =873643a(21) =1747627a(22) =3495595a(23) =6990507a(24) =13980331a(25) =27962027a(26) =55925419a(27) =111848107a(28) =223693483a(29) =447392427