a(n) = a(n-1) + 2*a(n-2) - a(n-3) - a(n-4), a(0)=0, a(1)=8, a(2)=10, a(3)=18.

Terms

a(0) =0a(1) =8a(2) =10a(3) =18a(4) =30a(5) =48a(6) =80a(7) =128a(8) =210a(9) =338a(10) =550a(11) =888a(12) =1440a(13) =2328a(14) =3770a(15) =6098a(16) =9870a(17) =15968a(18) =25840a(19) =41808a(20) =67650a(21) =109458a(22) =177110a(23) =286568a(24) =463680a(25) =750248a(26) =1213930a(27) =1964178a(28) =3178110a(29) =5142288