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id	challengeType	title	forumTopicId
5900f4621000cf542c50ff74	5	Problem 245: Coresilience	301892

Description

We shall call a fraction that cannot be cancelled down a resilient fraction. Furthermore we shall define the resilience of a denominator, R(d), to be the ratio of its proper fractions that are resilient; for example, R(12) = 4⁄11.

The resilience of a number d > 1 is then φ(d)d − 1 , where φ is Euler's totient function. We further define the coresilience of a number n > 1 as C(n)= n − φ(n)n − 1. The coresilience of a prime p is C(p) = 1p − 1. Find the sum of all composite integers 1 < n ≤ 2×1011, for which C(n) is a unit fraction.

Instructions

Tests

tests:
  - text: <code>euler245()</code> should return 288084712410001.
    testString: assert.strictEqual(euler245(), 288084712410001);

Challenge Seed

function euler245() {
  // Good luck!
  return true;
}

euler245();

Solution

// solution required

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