985 B
985 B
id | title | challengeType | forumTopicId | dashedName |
---|---|---|---|---|
5900f52c1000cf542c51003e | Problem 447: Retractions C | 5 | 302119 | problem-447-retractions-c |
--description--
For every integer n > 1
, the family of functions f_{n, a, b}
is defined by:
f_{n, a, b}(x) ≡ ax + b\bmod n
for a, b, x
integer and 0 \lt a \lt n
, 0 \le b \lt n
, 0 \le x \lt n
.
We will call f_{n, a, b}
a retraction if f_{n, a, b}(f_{n, a, b}(x)) \equiv f_{n, a, b}(x)\bmod n
for every 0 \le x \lt n
.
Let R(n)
be the number of retractions for n
.
F(N) = \displaystyle\sum_{n = 2}^N R(n)
.
F({10}^7) ≡ 638\\,042\\,271\bmod 1\\,000\\,000\\,007
.
Find F({10}^{14})
. Give your answer modulo 1\\,000\\,000\\,007
.
--hints--
retractionsC()
should return 530553372
.
assert.strictEqual(retractionsC(), 530553372);
--seed--
--seed-contents--
function retractionsC() {
return true;
}
retractionsC();
--solutions--
// solution required