Problem #27 Difficulty: 5%

Quadratic Primes

Solution Language: Java

Problem Statement

Euler discovered the remarkable quadratic formula:

n² + n + 41

It turns out that the formula will produce 40 primes for the consecutive integer values 0 ≤ n ≤ 39. However, when n = 40, 40² + 40 + 41 = 40(40 + 1) + 41 is divisible by 41, and certainly when n = 41, 41² + 41 + 41 is clearly divisible by 41.

The incredible formula n² - 79n + 1601 was discovered, which produces 80 primes for the consecutive values 0 ≤ n ≤ 79. The product of the coefficients, -79 and 1601, is -126479.

Considering quadratics of the form:

n² + an + b, where |a| < 1000 and |b| ≤ 1000

Find the product of the coefficients, a and b, for the quadratic expression that produces the maximum number of primes for consecutive values of n, starting with n = 0.

Approach

The solution involves:

  1. Testing all combinations of a and b within the given ranges
  2. For each combination, counting consecutive primes starting from n = 0
  3. Using a prime checking function to validate each result
  4. Tracking the coefficients that produce the maximum consecutive primes