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1.0 KiB
id | title | challengeType | forumTopicId | dashedName |
---|---|---|---|---|
5900f52a1000cf542c51003c | Problem 445: Retractions A | 5 | 302117 | problem-445-retractions-a |
--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
.
You are given that
\sum_{k = 1}^{99\\,999} R(\displaystyle\binom{100\\,000}{k}) \equiv 628\\,701\\,600\bmod 1\\,000\\,000\\,007
Find \sum_{k = 1}^{9\,999\,999} R(\displaystyle\binom{10\,000\,000}{k})
Give your answer modulo
1\\,000\\,000\\,007
.
--hints--
retractionsA()
should return 659104042
.
assert.strictEqual(retractionsA(), 659104042);
--seed--
--seed-contents--
function retractionsA() {
return true;
}
retractionsA();
--solutions--
// solution required