Number of reversible strings with n beads using exactly three different colors.

A056310

Number of reversible strings with n beads using exactly three different colors.

Terms

    a(0) =0a(1) =0a(2) =3a(3) =18a(4) =78a(5) =273a(6) =921a(7) =2916a(8) =9150a(9) =28065a(10) =85773a(11) =259848a(12) =785778a(13) =2367813a(14) =7128201a(15) =21427956a(16) =64382550a(17) =193326105a(18) =580372293a(19) =1741847328a(20) =5227116378a(21) =15684323853a(22) =47059266081a(23) =141189861996

External references