Project Euler Q28 - LO Man Hei

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   "source": [
    "### Q28\n",
    "What is the sum of the numbers on the diagonals in a 1001 by 1001 spiral formed in the same way?"
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    "def sum_of_square_first_n(n):\n",
    "    return (n)*(n+1)*(2*n+1)//6\n",
    "\n",
    "def sum_of_first_n(n):\n",
    "    return (1+n)*n//2\n",
    "\n",
    "def sum_diag_odd_spiral(n):\n",
    "    if n % 2 == 0:\n",
    "        print(\"'n' is even.\")\n",
    "        return None\n",
    "    return 4*(4*sum_of_square_first_n((n-1)//2) + sum_of_first_n((n-1)//2) + ((n-1)//2)) + 1\n",
    "    "
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      "CPU times: user 4 µs, sys: 0 ns, total: 4 µs\n",
      "Wall time: 5.25 µs\n"
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   "source": [
    "%%time\n",
    "sum_diag_odd_spiral(1001)"
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