A056521 Number of primitive (period n) periodic palindromic structures using exactly four different symbols.

0, 0, 0, 0, 0, 1, 1, 7, 10, 43, 65, 219, 350, 1058, 1701, 4796, 7770, 21094, 34105, 90205, 145749, 379326, 611501, 1573205, 2532530, 6465123, 10391735, 26378849, 42355950, 107089814, 171798901, 433088656, 694337225, 1746623215, 2798806984, 7029320466, 11259666950

Offset: 1

Author

Marks R. Nester

Keywords

• nonn

Examples

			For example, aaabbb is not a (finite) palindrome but it is a periodic palindrome. Permuting the symbols 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]

Links

• Andrew Howroyd, Table of n, a(n) for n = 1..200

Crossrefs

Column 4 of A285037.

Cf. A056483, A056510, A056514, A056515.

Formula

a(n) = A056515(n) - A056514(n).

Moebius transform of A056510. - T. D. Noe, Oct 25 2006

Extensions

Corrected by T. D. Noe, Oct 25 2006

a(17)-a(30) from Andrew Howroyd, Apr 08 2017

Terms a(31) and beyond from Andrew Howroyd, Oct 01 2019