988 B
988 B
id | title | challengeType | forumTopicId | dashedName |
---|---|---|---|---|
5900f4621000cf542c50ff74 | Problem 245: Coresilience | 5 | 301892 | problem-245-coresilience |
--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.
--hints--
euler245()
should return 288084712410001.
assert.strictEqual(euler245(), 288084712410001);
--seed--
--seed-contents--
function euler245() {
return true;
}
euler245();
--solutions--
// solution required