OFFSET
1,2
COMMENTS
The n where the decimal expansion of 1/n has a period length which is a power of 2.
REFERENCES
J. W. L. Glaisher, On circulating decimals, Proc. Camb. Phil. Soc., 3 (1878), 185-206.
D. H. Lehmer, Guide to Tables in the Theory of Numbers. Bulletin No. 105, National Research Council, Washington, DC, 1941, pp. 7-12.
LINKS
Eric Weisstein's World of Mathematics, Decimal Expansion.
EXAMPLE
Period of 1/3 = 1. Period of 1/9 = 2. Period of 1/73 = 8. Period of 1/353 = 32.
MAPLE
A084680 := proc(n) if gcd(n, 10) <> 1 then 0 ; elif n = 1 then 1 ; else numtheory[order](10, n) ; end if; end proc:
isA000079 := proc(n) if n = 1 then true; elif n >=1 then numtheory[factorset](n) = {2} ; else false; end if; end proc:
for n from 1 to 5000 do if isA000079(A084680(n)) then printf("%d, ", n) ; end if; end do: # R. J. Mathar, Mar 10 2010
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Feb 17 2010
EXTENSIONS
Missing numbers -those where A084680(n)>1000- inserted - R. J. Mathar, Mar 10 2010
STATUS
approved