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 A005819 Number of words of length n in a certain language. (Formerly M1584) 10
 1, 2, 6, 12, 22, 34, 52, 74, 102, 134, 176, 222, 280, 344, 416, 496, 592, 694, 814, 942, 1082, 1232, 1404, 1584, 1784, 1996, 2226, 2468, 2738, 3016, 3324, 3648, 3992, 4352, 4736, 5132, 5564, 6014, 6488, 6978, 7508, 8050, 8634, 9238, 9866, 10516, 11212 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 REFERENCES N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Herman Jamke, Table of n, a(n) for n = 1..100 J. Berstel and M. Pocchiola, A geometric proof of the enumeration formula for Sturmian words, Internat. J. Algeb. Comput., 3(3):349-355, 1993. - Herman Jamke (hermanjamke(AT)fastmail.fm), Mar 02 2008 S. Dulucq, Etude combinatoire de problèmes d'énumération, d'algorithmique sur les arbres et de codage par des mots, a thesis presented to l'Université de Bordeaux I, 1987. (Annotated scanned copy) S. Dulucq and D. Gouyou-Beauchamps, Sur les facteurs des suites de Sturm, Theoret. Comput. Sci. 71 (1990), 381-400. FORMULA a(n) = -1 + Sum_{i=1..n} (n-i+1)*phi(i) for n>=2, where phi is Euler's totient function (this is conjectured in the Duluck & Gouyou-Beauchamps paper, p. 399). PROG (PARI) a(n)=if(n<2, n>0, sum(i=1, n, (n-i+1)*eulerphi(i))-1) \\ Herman Jamke (hermanjamke(AT)fastmail.fm), Mar 02 2008 CROSSREFS Sequence in context: A147623 A232234 A045964 * A304627 A168193 A182977 Adjacent sequences:  A005816 A005817 A005818 * A005820 A005821 A005822 KEYWORD nonn AUTHOR EXTENSIONS More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Mar 02 2008 STATUS approved

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Last modified September 24 20:09 EDT 2018. Contains 315356 sequences. (Running on oeis4.)