a(n) = a(n-1) + a(n-2) + a(n-3) with a(0)=2, a(1)=1, a(2)=2.

Terms

a(0) =2a(1) =1a(2) =2a(3) =5a(4) =8a(5) =15a(6) =28a(7) =51a(8) =94a(9) =173a(10) =318a(11) =585a(12) =1076a(13) =1979a(14) =3640a(15) =6695a(16) =12314a(17) =22649a(18) =41658a(19) =76621a(20) =140928a(21) =259207a(22) =476756a(23) =876891a(24) =1612854a(25) =2966501a(26) =5456246a(27) =10035601a(28) =18458348a(29) =33950195