Number of degree-n permutations of order dividing 3.

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =9a(5) =21a(6) =81a(7) =351a(8) =1233a(9) =5769a(10) =31041a(11) =142011a(12) =776601a(13) =4874013a(14) =27027729a(15) =168369111a(16) =1191911841a(17) =7678566801a(18) =53474964993a(19) =418199988339