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 A056504 Number of periodic palindromic structures of length n using a maximum of three different symbols. 5
 1, 1, 2, 2, 5, 5, 12, 14, 33, 41, 90, 122, 259, 365, 756, 1094, 2233, 3281, 6642, 9842, 19813, 29525, 59292, 88574, 177527, 265721, 532170, 797162, 1595443, 2391485, 4785156, 7174454, 14352233, 21523361, 43053282, 64570082, 129150085, 193710245, 387440172, 581130734, 1162291121 (list; graph; refs; listen; history; text; internal format)
 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 Andrew Howroyd, Table of n, a(n) for n = 0..200 FORMULA a(n) = Sum_{k=1..3} A285012(n, k) for n > 0. - Andrew Howroyd, Oct 01 2019 CROSSREFS Cf. A007051, A285012. Sequence in context: A097896 A030223 A300436 * A122205 A338762 A178115 Adjacent sequences:  A056501 A056502 A056503 * A056505 A056506 A056507 KEYWORD nonn AUTHOR EXTENSIONS a(17)-a(35) from Andrew Howroyd, Apr 07 2017 a(0)=1 prepended and terms a(36) and beyond from Andrew Howroyd, Oct 01 2019 STATUS approved

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Last modified May 17 00:16 EDT 2021. Contains 343957 sequences. (Running on oeis4.)