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A056505
Number of periodic palindromic structures using a maximum of four different symbols.
5
1, 1, 2, 2, 5, 5, 13, 15, 40, 51, 133, 187, 479, 715, 1815, 2795, 7036, 11051, 27747, 43947, 110061, 175275, 438683, 700075, 1750959, 2798251, 6997643, 11188907, 27975351, 44747435, 111876715, 178973355, 447445692, 715860651, 1789684267, 2863377067, 7158491875
OFFSET
0,3
COMMENTS
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
FORMULA
a(n) = Sum_{k=1..4} A285012(n, k) for n > 0. - Andrew Howroyd, Oct 01 2019
CROSSREFS
Sequence in context: A094967 A322111 A321395 * A056506 A056507 A285013
KEYWORD
nonn
EXTENSIONS
Corrected by T. D. Noe, Oct 25 2006
a(0)=1 prepended and terms a(17) and beyond from Andrew Howroyd, Oct 01 2019
STATUS
approved