euler/ipython/EulerProblem047.ipynb

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   "source": [
    "# Distinct primes factors (Euler Problem 47)"
   ]
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   "source": [
    "[https://projecteuler.net/problem=47](https://projecteuler.net/problem=47)\n",
    "\n",
    "The first two consecutive numbers to have two distinct prime factors are:\n",
    "\n",
    "14 = 2 × 7\n",
    "\n",
    "15 = 3 × 5\n",
    "\n",
    "The first three consecutive numbers to have three distinct prime factors are:\n",
    "\n",
    "644 = 2² × 7 × 23\n",
    "\n",
    "645 = 3 × 5 × 43\n",
    "\n",
    "646 = 2 × 17 × 19.\n",
    "\n",
    "Find the first four consecutive integers to have four distinct prime factors each. What is the first of these numbers?"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 46,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[2, 3, 7]\n"
     ]
    }
   ],
   "source": [
    "def sieve_of_eratosthenes(number):\n",
    "    primes = []\n",
    "    prospects = [n for n in range(2, number + 1)]\n",
    "    while prospects:\n",
    "        p = prospects[0]\n",
    "        prospects = [x for x in prospects if x % p != 0]\n",
    "        primes.append(p)\n",
    "        if p * p > number:\n",
    "            break\n",
    "    return primes + prospects\n",
    "\n",
    "import math\n",
    "\n",
    "def get_prime_factors(n):\n",
    "    ps = sieve_of_eratosthenes(n)\n",
    "    fs = []\n",
    "    for p in ps:\n",
    "        if n % p == 0:\n",
    "            fs.append(p)\n",
    "        while n % p == 0:\n",
    "            n = n // p\n",
    "    return fs\n",
    "\n",
    "def trial_division(n):\n",
    "    a = []  \n",
    "    if n % 2 == 0:\n",
    "        a.append(2)\n",
    "    while n % 2 == 0:\n",
    "        n //= 2\n",
    "    f = 3\n",
    "    while f * f <= n:\n",
    "        if n % f == 0:\n",
    "            a.append(f)\n",
    "            while n % f == 0:\n",
    "                n //= f\n",
    "        else:\n",
    "            f += 2   \n",
    "    if n != 1:\n",
    "        a.append(n)\n",
    "    return a\n",
    "    \n",
    "assert(get_prime_factors(14) == [2, 7])\n",
    "assert(get_prime_factors(644) == [2, 7, 23])\n",
    "\n",
    "print(trial_division(126))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 54,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "134043\n"
     ]
    }
   ],
   "source": [
    "s = []\n",
    "for n in range(2, 1000000):\n",
    "    if len(trial_division(n)) == 4:\n",
    "        s.append(n)\n",
    "    else:\n",
    "        s = []\n",
    "    if len(s) == 4:\n",
    "        s = s[0]\n",
    "        break\n",
    "\n",
    "print(s)\n",
    "assert(s == 134043)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
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 "metadata": {
  "completion_date": "Sun, 23 Dec 2018, 00:24",
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  "tags": [
   "trial division",
   "prime",
   "brute force"
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