a(n) = A333650(n, 3) for n >= 3; a(1) = a(2) = 0.

Terms

a(0) =0a(1) =0a(2) =4a(3) =11a(4) =24a(5) =52a(6) =110a(7) =228a(8) =467a(9) =949a(10) =1916a(11) =3848a(12) =7696a(13) =15342a(14) =30505a(15) =60527a(16) =119892a(17) =237156a(18) =468590a(19) =925032a(20) =1824727a(21) =3597289a(22) =7088216a(23) =13961168a(24) =27489168a(25) =54110618a(26) =106489245a(27) =209531251a(28) =412217072a(29) =810865812