Number of strings over Z_3 of length n with trace 0 and subtrace 0.

Terms

a(0) =1a(1) =1a(2) =3a(3) =9a(4) =21a(5) =63a(6) =225a(7) =729a(8) =2187a(9) =6561a(10) =19845a(11) =59535a(12) =177633a(13) =531441a(14) =1594323a(15) =4782969a(16) =14344533a(17) =43033599a(18) =129127041a(19) =387420489a(20) =1162261467a(21) =3486784401a(22) =10460471301a(23) =31381413903a(24) =94143533121a(25) =282429536481a(26) =847288609443