a(n+1) - 3*a(n) + a(n-1) = (2/3)(1+w^(n+1)+w^(2n+2)), where w = exp(2 Pi I / 3).

Terms

a(0) =0a(1) =1a(2) =3a(3) =8a(4) =23a(5) =61a(6) =160a(7) =421a(8) =1103a(9) =2888a(10) =7563a(11) =19801a(12) =51840a(13) =135721a(14) =355323a(15) =930248a(16) =2435423a(17) =6376021a(18) =16692640a(19) =43701901a(20) =114413063a(21) =299537288a(22) =784198803a(23) =2053059121a(24) =5374978560a(25) =14071876561a(26) =36840651123a(27) =96450076808a(28) =252509579303