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本帖最后由 欧拉计划 于 2017-1-5 15:25 编辑
Investigating the primality of numbers of the form 2n2-1
Consider numbers t(n) of the form t(n) = 2n2-1 with n > 1.
The first such numbers are 7, 17, 31, 49, 71, 97, 127 and 161.
It turns out that only 49 = 7*7 and 161 = 7*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 ?
题目:
对于形如 t(n) = 2n2-1, n > 1 的数字 t(n) 来说,前几个分别是 7, 17, 31, 49, 71, 97, 127 和 161,可知,只有 49 = 7*7 以及 161 = 7*23 不是素数。在 n ≤ 10000 的范围内,一共有 2202 个 t(n) 是素数。
请问,在 n ≤ 50,000,000 范围内,有多少个 t(n) 是素数?
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