OFFSET
1,1
COMMENTS
Conjecture proposed by the authors in References page 205: if p is a prime with gcd(p,30) = 1 and if the period of 1/p is m then the period of 1/p^n is m*p^(n-1).
REFERENCES
J.-M. De Koninck & A. Mercier, 1001 Problèmes en Théorie Classique des Nombres, Problème 346 pp. 50, 204-205, Ellipses, Paris 2004.
EXAMPLE
1/121 = 0. 0082644628099173553719 0082644628099173553719 ... with periodic part {0082644628099173553719}, whose length is 22 digits, so a(2) = 22.
MATHEMATICA
MultiplicativeOrder[10, 11^#] & /@ Range[20] (* Giovanni Resta, May 07 2020 *)
PROG
(PARI) a(n) = znorder(Mod(10, 11^n)); \\ Michel Marcus, May 09 2020
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Bernard Schott, May 07 2020
EXTENSIONS
More terms from Giovanni Resta, May 07 2020
STATUS
approved