If you consider any multiple of 3 and then sum up its digits, the sum is always divisible by 3. For eg. 843 is a multiple of 3 and 8 + 4 + 3 = 15 is also multiple of 3. Similarly, for 9, any multiple of 9 satisfies the property that the sum of its digits is also divisible by 9.
But he suddenly realized that this property for 3 or 9 in base 10 may not hold for another base (let say 11)
Inquisitive, that he is, he wants to know the number of digits for which this property holds for a particular base non trivially.
For 0 and 1, this property holds trivially and thus can be ignored.
A base is the number of unique digits, including zero, that is used to represent numbers .
i am unable to get it... please give some hints.