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
KEYWORD
nonn
AUTHOR
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Mar 02 2008
STATUS
approved