Twin Prime Pairs

Difficulty: 1400 3000 ms 128 MB

math number-theory

Count the twin prime pairs (p, p+2) with both members ≤ N.

Input: one integer N.

Output: the number of twin prime pairs with p+2 ≤ N.

Constraints:

• 1 ≤ N ≤ 10⁶

Sample Tests

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