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

Terms

a(0) =1a(1) =2a(2) =3a(3) =10a(4) =22a(5) =51a(6) =125a(7) =293a(8) =696a(9) =1657a(10) =3928a(11) =9330a(12) =22157a(13) =52601a(14) =124905a(15) =296578a(16) =704191a(17) =1672062a(18) =3970178a(19) =9426875a(20) =22383417a(21) =53147701a(22) =126195160a(23) =299640813a(24) =711474236a(25) =1689341342a(26) =4011212253a(27) =9524317645a(28) =22614766177a(29) =53697038226