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

Terms

a(0) =1a(1) =2a(2) =2a(3) =5a(4) =9a(5) =16a(6) =30a(7) =55a(8) =101a(9) =186a(10) =342a(11) =629a(12) =1157a(13) =2128a(14) =3914a(15) =7199a(16) =13241a(17) =24354a(18) =44794a(19) =82389a(20) =151537a(21) =278720a(22) =512646a(23) =942903a(24) =1734269a(25) =3189818a(26) =5866990a(27) =10791077a(28) =19847885a(29) =36505952