Number of primitive (aperiodic) reversible string structures with n beads using a maximum of four different colors.

A056333

Number of primitive (aperiodic) reversible string structures with n beads using a maximum of four different colors.

Terms

    a(0) =1a(1) =1a(2) =3a(3) =9a(4) =30a(5) =102a(6) =378a(7) =1440a(8) =5607a(9) =22155a(10) =87978a(11) =350775a(12) =1400490a(13) =5597487a(14) =22379145a(15) =89498880a(16) =357952170a(17) =1431737433a(18) =5726775978a(19) =22906819575a(20) =91626580269a(21) =366505186047

External references