a(n) = 3*a(n-1) - a(n-3) + 3*a(n-4), with initial values 1,4,14,41.

Terms

a(0) =1a(1) =4a(2) =14a(3) =41a(4) =122a(5) =364a(6) =1093a(7) =3280a(8) =9842a(9) =29525a(10) =88574a(11) =265720a(12) =797161a(13) =2391484a(14) =7174454a(15) =21523361a(16) =64570082a(17) =193710244a(18) =581130733a(19) =1743392200a(20) =5230176602a(21) =15690529805a(22) =47071589414a(23) =141214768240a(24) =423644304721