=
Certainly the denominator 3n is greater than n. Therefore
the fraction must reduce. Thus let d > 1 be the greatest
common divisor of n+3 and 3n, the numerator and denominator.
Then there exist positive integers k,m such that
n+3 = kd and 3n = md
So the fraction
reduces to
, where m < n.
Then n = kd-3, and by substitution
3(kd-3) = md
3kd - 9 = md
3kd-md = 9
d(3k-m) = 9
d =
So 3k-m is a divisor of 9, either 1, 3, or 9.
Since d > 1, 3k-m ≠ 9. So d is one of the
other two possibilities, d=3 or d=9
If d=3, then 3k-m = 3
3k = m+3
k =
Since n+3 = kd,
n+3 =
*3
n+3 = m+3
n = m
But that contradicts m < n
So d=9, and 3k-m = 1
m = 3k-1
3n = md = dm
3n = 9(3k-1)
n = 3(3k-1)
n = 9k-3
Therefore n must be in the sequence 6,15,24,...,9k-3,...
n = 9k-3 ≤ 2015
9k ≤ 2018
k ≤ 224.2222...
So maximum value of k is 224,
thus the answer is 224.
Edwin