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) | = | 1 p − 1 | . |
Find the sum of all composite integers 1 < n ≤ 2×1011, for which C(n) is a unit fraction.