When Meena turned 16 years old, her parents gave her a cake with candles, where has exactly 16 different positive integer divisors. What is the smallest possible value of ?
Solution
To find the smallest possible value of that has exactly 16 different positive integer divisors, we need to consider the number of divisors function. For a number with prime factorization , the number of divisors is given by:
We need . The possible factorizations of 16 are:
1.
2.
3.
4.
5.
We will consider each case to find the smallest .
Case 1:
- The smallest prime is 2.
-
Case 2:
- The smallest primes are 2 and 3.
-
Case 3:
- The smallest primes are 2 and 3.
-
Case 4:
- The smallest primes are 2, 3, and 5.
-
Case 5:
- The smallest primes are 2, 3, 5, and 7.
-
Among these cases, the smallest value of is found in Case 4:
Thus, the smallest possible value of that has exactly 16 different positive integer divisors is .
Want a route through all this instead of an archive? The track
puts 2,000 problems in a working order, from AMC 10 level to the IMO shortlist.