yaworsw/euler-manager

---
:id: 216
:name: Investigating the primality of numbers of the form 2<var>n</var><sup>2</sup>-1
:url: https://projecteuler.net/problem=216
:content: "Consider numbers <var>t</var>(<var>n</var>) of the form <var>t</var>(<var>n</var>)
  = 2<var>n</var><sup>2</sup>-1 with <var>n</var> \\> 1.  \nThe first such numbers
  are 7, 17, 31, 49, 71, 97, 127 and 161.  \nIt turns out that only 49 = 7\\*7 and
  161 = 7\\*23 are not prime.  \nFor <var>n</var> ≤ 10000 there are 2202 numbers <var>t</var>(<var>n</var>)
  that are prime.\n\nHow many numbers <var>t</var>(<var>n</var>) are prime for <var>n</var>
  ≤ 50,000,000 ?\n\n"