Generalized Euler phi function (for p=3).

Terms

a(0) =1a(1) =4a(2) =18a(3) =32a(4) =160a(5) =324a(6) =1456a(7) =2048a(8) =13122a(9) =25600a(10) =117128a(11) =209952a(12) =913952a(13) =2119936a(14) =9447840a(15) =13107200a(16) =86093440a(17) =172186884a(18) =774840976a(19) =1310720000a(20) =6964002864a(21) =13718968384a(22) =62761410632a(23) =88159684608a(24) =557885504000a(25) =835308258304