887 B
887 B
id | title | challengeType | forumTopicId | dashedName |
---|---|---|---|---|
5900f4451000cf542c50ff57 | Problem 216: Investigating the primality of numbers of the form 2n2-1 | 5 | 301858 | problem-216-investigating-the-primality-of-numbers-of-the-form-2n2-1 |
--description--
Consider numbers t(n)
of the form t(n) = 2n^2 - 1
with n > 1
.
The first such numbers are 7, 17, 31, 49, 71, 97, 127 and 161.
It turns out that only 49 = 7 \times 7
and 161 = 7 \times 23
are not prime.
For n ≤ 10000
there are 2202 numbers t(n)
that are prime.
How many numbers t(n)
are prime for n ≤ 50\\,000\\,000
?
--hints--
primalityOfNumbers()
should return 5437849
.
assert.strictEqual(primalityOfNumbers(), 5437849);
--seed--
--seed-contents--
function primalityOfNumbers() {
return true;
}
primalityOfNumbers();
--solutions--
// solution required