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- #!/usr/bin/ruby
- # Author: Daniel "Trizen" Șuteu
- # License: GPLv3
- # Website: https://github.com/trizen
- # General formula: n^9 + n^6 * p = (n^3 + n^2)^3 where p is a prime number.
- # From the above formula results that p must have the form: 3n^2 + 3n + 1.
- # https://projecteuler.net/problem=131
- # Runtime: 0.110s
- var count = 0
- for (var n = 1; true ; ++n) {
- var p = (3*n**2 + 3*n + 1)
- p < 1e6 || break
- p.is_prime && ++count
- }
- say count
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