OFFSET
1,2
LINKS
Index entries for linear recurrences with constant coefficients, signature (3,-3,3,-2).
FORMULA
Limit_{n -> oo} a(n+1)/a(n) = 2.
a(n) = [(9/10)*2^n]. - David W. Wilson, Jun 18 2009
G.f.: x * ( 1+x^2-x^3 ) / ( (x-1)*(2*x-1)*(x^2+1) ). - R. J. Mathar, Feb 20 2011
EXAMPLE
a(1)=1 because 5 divides only 5,
a(2)=3 because 25 divides {25, 50 & 75},
a(3)=7 because 125 divides {125, 250, 375, 500, 625, 750 & 925}, etc.
MATHEMATICA
f[n_] := Floor[(10^n - 1)/5^n] - Floor[10^(n - 1)/5^n]; Array[f, 35]
LinearRecurrence[{3, -3, 3, -2}, {1, 3, 7, 14}, 30] (* Harvey P. Dale, Feb 20 2016 *)
CROSSREFS
KEYWORD
nonn,base,easy
AUTHOR
Robert G. Wilson v, Jun 17 2009
STATUS
approved