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 A280303 Number of binary necklaces of length n with no subsequence 00000. 4
 1, 2, 3, 5, 7, 12, 17, 31, 51, 91, 155, 287, 505, 930, 1695, 3129, 5759, 10724, 19913, 37239, 69643, 130745, 245715, 463099, 873705, 1651838, 3126707, 5927817, 11251031, 21382558, 40679233, 77475673, 147694719 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(n) is the number of cyclic sequences of length n consisting of zeros and ones that do not contain five consecutive zeros provided we consider as equivalent those sequences that are cyclic shifts of each other. LINKS P. Flajolet and M. Soria, The Cycle Construction, SIAM J. Discr. Math., vol. 4 (1), 1991, pp. 58-60. Petros Hadjicostas, Proof of the formula for the generating function from the formula for a(n) F. Ruskey, Necklaces, Lyndon words, De Bruijn sequences, etc. [Cached copy, with permission, pdf format only] L. Zhang and P. Hadjicostas, On sequences of independent Bernoulli trials avoiding the pattern '11..1', Math. Scientist, 40 (2015), 89-96. FORMULA a(n) = (1/n) * Sum_{d divides n} totient(n/d) * A074048(d). G.f.: Sum_{k>=1} (phi(k)/k) * log(1/(1-B(x^k))) where B(x) = x*(1+x+x^2+x^3+x^4). EXAMPLE a(5)=7 because we have seven binary cyclic sequences (necklaces) of length 5 that avoid five consecutive zeros: 00001, 00011, 00101, 00111, 01101, 01111, 11111. CROSSREFS Cf. A000358, A093305, A280218, A074048. Sequence in context: A206290 A091696 A334683 * A048808 A263358 A239915 Adjacent sequences:  A280300 A280301 A280302 * A280304 A280305 A280306 KEYWORD nonn AUTHOR Petros Hadjicostas and Lingyun Zhang, Dec 31 2016 STATUS approved

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Last modified December 3 12:38 EST 2021. Contains 349463 sequences. (Running on oeis4.)