Consecutive Primes
InterviewTime limit15sMemory limit1024 MB
For each query Z, find the largest product of two consecutive primes that does not exceed Z.
- Level
Medium4 of 10
- Topics
- Number theory, Math, Binary search, Brute force
- Solved
- No attempts yet
Problem
Ada has bought a secret present for her friend John. To open the present, John must crack a secret code. Ada decides to give him a hint to make things simple for him. She tells him that the secret code is a number that can be formed by taking the product of two consecutive prime numbers, such that it is the largest number that is smaller than or equal to . Given the value of , help John determine the secret code.
Formally, let the order of prime numbers 2, 3, 5, 7, 11, ... be denoted by , , , , , ... and so on. Consider to be the product of two consecutive primes and . The secret code is the largest such that .
Input
The first line of the input gives the number of test cases, . lines follow.
Each line contains a single integer , the number Ada gives as part of the hint.
Output
For each test case, output one line containing Case #x: y, where is the test case number (starting from 1) and is the secret code, the largest number less than or equal to that is the product of two consecutive prime numbers.
Limits
- .
Hint
For sample case #1, the secret code is 2021 because it is exactly the product of consecutive primes 43 and 47.
For sample case #2, the secret code is 1763 because the product of 41 and 43 is 1763, which is smaller than 2020, but the product of 43 and 47 exceeds the given value 2020.