a(n) = 2*a(n-1) + a(n-2) + a(n-3) + a(n-4), with a(0)=1, a(1)=2, a(3)=5, a(4)=13.

Terms

a(0) =1a(1) =2a(2) =5a(3) =13a(4) =34a(5) =88a(6) =228a(7) =591a(8) =1532a(9) =3971a(10) =10293a(11) =26680a(12) =69156a(13) =179256a(14) =464641a(15) =1204374a(16) =3121801a(17) =8091873a(18) =20974562a(19) =54367172a(20) =140922580a(21) =365278767a(22) =946821848a(23) =2454212215a(24) =6361447625a(25) =16489208080a(26) =42740897848a(27) =110786663616a(28) =287164880785a(29) =744346531114