3770. Largest Prime from Consecutive Prime Sum
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You are given an integer n.
Return the largest prime number less than or equal to n that can be expressed as the sum of one or more consecutive prime numbers starting from 2. If no such number exists, return 0.
Example 1:
Input: n = 20
Output: 17
Explanation:
The prime numbers less than or equal to n = 20 which are consecutive prime sums are:
-
2 = 2 -
5 = 2 + 3 -
17 = 2 + 3 + 5 + 7
The largest is 17, so it is the answer.
Example 2:
Input: n = 2
Output: 2
Explanation:
The only consecutive prime sum less than or equal to 2 is 2 itself.
Constraints:
1 <= n <= 5 * 105
Hints
Hint 1
Generate all prime numbers up to
n (use sieve or trial division).Hint 2
Compute consecutive sums starting from 2 until the sum exceeds
n.Hint 3
Find the largest sum that is also a prime.