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

Terms

a(0) =1a(1) =4a(2) =10a(3) =23a(4) =53a(5) =123a(6) =286a(7) =665a(8) =1546a(9) =3594a(10) =8355a(11) =19423a(12) =45153a(13) =104968a(14) =244021a(15) =567280a(16) =1318766a(17) =3065759a(18) =7127025a(19) =16568323a(20) =38516678a(21) =89540413a(22) =208156206a(23) =483904470a(24) =1124941411a(25) =2615171499a(26) =6079536145a(27) =14133206848a(28) =32855719753a(29) =76380281708