Number of identity bracelets of n beads of 3 colors.

Terms

a(0) =3a(1) =3a(2) =1a(3) =3a(4) =12a(5) =37a(6) =117a(7) =333a(8) =975a(9) =2712a(10) =7689a(11) =21414a(12) =60228a(13) =168597a(14) =475024a(15) =1338525a(16) =3788400a(17) =10741575a(18) =30556305a(19) =87109332a(20) =248967446a(21) =713025093a(22) =2046325125a(23) =5883406830a(24) =16944975036a(25) =48880411272a(26) =141212376513