a(n+3) = 3*a(n+2) - 2*a(n+1) + a(n).

Terms

a(0) =1a(1) =3a(2) =7a(3) =16a(4) =37a(5) =86a(6) =200a(7) =465a(8) =1081a(9) =2513a(10) =5842a(11) =13581a(12) =31572a(13) =73396a(14) =170625a(15) =396655a(16) =922111a(17) =2143648a(18) =4983377a(19) =11584946a(20) =26931732a(21) =62608681a(22) =145547525a(23) =338356945a(24) =786584466a(25) =1828587033a(26) =4250949112a(27) =9882257736a(28) =22973462017a(29) =53406819691