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    "# Spiral primes (Euler Problem 58)"
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    "[https://projecteuler.net/problem=58](https://projecteuler.net/problem=58)\n",
    "\n",
    "Starting with 1 and spiralling anticlockwise in the following way, a square spiral with side length 7 is formed.\n",
    "\n",
    "37 36 35 34 33 32 31\n",
    "38 17 16 15 14 13 30\n",
    "39 18  5  4  3 12 29\n",
    "40 19  6  1  2 11 28\n",
    "41 20  7  8  9 10 27\n",
    "42 21 22 23 24 25 26\n",
    "43 44 45 46 47 48 49\n",
    "\n",
    "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%.\n",
    "\n",
    "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%?"
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