Number of primitive (period n) n-bead necklaces with exactly three different colored beads.

Terms

a(0) =0a(1) =0a(2) =2a(3) =9a(4) =30a(5) =89a(6) =258a(7) =720a(8) =2016a(9) =5583a(10) =15546a(11) =43215a(12) =120750a(13) =338001a(14) =950030a(15) =2677770a(16) =7573350a(17) =21478632a(18) =61088874a(19) =174179133a(20) =497812378a(21) =1425832077a(22) =4092087522a(23) =11765778330a(24) =33887517840a(25) =97756266615a(26) =282414622728a(27) =816999371955