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 # Spiral primes
 [Problem 58](https://projecteuler.net/problem=58) - Diifculty level: 5%

 Starting with 1 and spiralling anticlockwise in the following way, a square spiral with side length 7 is formed.

 ![](58-1.png)

 It is interesting to note that the odd squares lie along the bottom right diagonal, but what is more interesting is that 8 out of the 13 numbers lying along both diagonals are prime; that is, a ratio of 8/13 ≈ 62%.

 If one complete new layer is wrapped around the spiral above, a square spiral with side length 9 will be formed. If this process is continued, what is the side length of the square spiral for which the ratio of primes along both diagonals first falls below 10%?
 */
