Number of closed paths of length n whose steps are 9th roots of unity, U_9(n).

Terms

a(0) =1a(1) =0a(2) =0a(3) =18a(4) =0a(5) =0a(6) =2430a(7) =0a(8) =0a(9) =640080a(10) =0a(11) =0a(12) =215488350a(13) =0a(14) =0a(15) =84569753268a(16) =0a(17) =0a(19) =0a(20) =0a(22) =0a(23) =0a(25) =0a(26) =0a(28) =0a(29) =0a(31) =0a(32) =0