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 A056521 Number of primitive (period n) periodic palindromic structures using exactly four different symbols. 4
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,8 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 FORMULA a(n) = A056515(n) - A056514(n). Moebius transform of A056510. - T. D. Noe, Oct 25 2006 EXAMPLE For example, aaabbb is not a (finite) palindrome but it is a periodic palindrome. Permuting the symbols will not change the structure. CROSSREFS Column 4 of A285037. Cf. A056483, A056510, A056514, A056515. Sequence in context: A126076 A258284 A099579 * A056510 A013398 A013493 Adjacent sequences:  A056518 A056519 A056520 * A056522 A056523 A056524 KEYWORD nonn AUTHOR 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 STATUS approved

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Last modified October 23 12:54 EDT 2019. Contains 328345 sequences. (Running on oeis4.)