Question about the master theorem

Consider the regularity condition a*f(n/b) ? c*f(n) for some constant c < 1, which is part of case
3 of the master theorem. Give an example of constants a >= 1 and b > 1 and a function f(n) that
satisfies all the conditions in case 3 of the master theorem except the regularity condition.


for description of the master theorem see:
http://www.columbia.edu/~cs2035/courses/csor4231.F03/recurrences.pdf