1013 B
1013 B
id | title | challengeType | forumTopicId | dashedName |
---|---|---|---|---|
5900f45f1000cf542c50ff71 | Problem 242: Odd Triplets | 5 | 301889 | problem-242-odd-triplets |
--description--
Given the set {1,2,...,n}, we define f(n,k) as the number of its k-element subsets with an odd sum of elements. For example, f(5,3) = 4, since the set {1,2,3,4,5} has four 3-element subsets having an odd sum of elements, i.e.: {1,2,4}, {1,3,5}, {2,3,4} and {2,4,5}.
When all three values n, k and f(n,k) are odd, we say that they make an odd-triplet [n,k,f(n,k)].
There are exactly five odd-triplets with n ≤ 10, namely: [1,1,f(1,1) = 1], [5,1,f(5,1) = 3], [5,5,f(5,5) = 1], [9,1,f(9,1) = 5] and [9,9,f(9,9) = 1].
How many odd-triplets are there with n ≤ 1012 ?
--hints--
euler242()
should return 997104142249036700.
assert.strictEqual(euler242(), 997104142249036700);
--seed--
--seed-contents--
function euler242() {
return true;
}
euler242();
--solutions--
// solution required