A056337 Number of primitive (aperiodic) reversible string structures with n beads using exactly three different colors.

0, 0, 1, 4, 15, 49, 160, 498, 1544, 4715, 14356, 43420, 131145, 394990, 1188564, 3572400, 10732065, 32224216, 96733636, 290317660, 871200664, 2614083394, 7843255300, 23531731530, 70599259170, 211805771345

Offset: 1

Author

Marks R. Nester

Keywords

• nonn

Comments

A string and its reverse are considered to be equivalent. Permuting the colors will not change the structure.

References

• M. R. Nester (1999). Mathematical investigations of some plant interaction designs. PhD Thesis. University of Queensland, Brisbane, Australia. [See A056391 for pdf file of Chap. 2]

Crossrefs

Column 3 of A276544.

Cf. A056319.

Formula

A056332(n)-A056331(n).