Number of reversible string structures with n beads using a maximum of four different colors.

A056323

Number of reversible string structures with n beads using a maximum of four different colors.

Terms

    a(0) =1a(1) =1a(2) =2a(3) =4a(4) =11a(5) =31a(6) =107a(7) =379a(8) =1451a(9) =5611a(10) =22187a(11) =87979a(12) =350891a(13) =1400491a(14) =5597867a(15) =22379179a(16) =89500331a(17) =357952171a(18) =1431743147a(19) =5726775979a(20) =22906841771a(21) =91626580651a(22) =366505274027

External references