Number of primitive (aperiodic) reversible strings with n beads using exactly three different colors.

A056319

Number of primitive (aperiodic) reversible strings with n beads using exactly three different colors.

Terms

    a(0) =0a(1) =0a(2) =3a(3) =18a(4) =78a(5) =270a(6) =921a(7) =2898a(8) =9147a(9) =27987a(10) =85773a(11) =259557a(12) =785778a(13) =2366892a(14) =7128120a(15) =21425040a(16) =64382550a(17) =193316685a(18) =580372293a(19) =1741819245a(20) =5227115454a(21) =15684238080a(22) =47059266081a(23) =141189599250

External references