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   "source": [
    "# Euler Problem 25\n",
    "\n",
    "The Fibonacci sequence is defined by the recurrence relation:\n",
    "\n",
    "$F_n = F_{n−1} + F_{n−2}$, where $F_1 = 1$ and $F_2 = 1$.\n",
    "Hence the first 12 terms will be:\n",
    "\n",
    "~~~\n",
    "F1 = 1\n",
    "F2 = 1\n",
    "F3 = 2\n",
    "F4 = 3\n",
    "F5 = 5\n",
    "F6 = 8\n",
    "F7 = 13\n",
    "F8 = 21\n",
    "F9 = 34\n",
    "F10 = 55\n",
    "F11 = 89\n",
    "F12 = 144\n",
    "~~~\n",
    "\n",
    "The 12th term, $F_{12}$, is the first term to contain three digits.\n",
    "\n",
    "What is the index of the first term in the Fibonacci sequence to contain 1000 digits?"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Reuse fibonacci generator and then straight forward."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "4782\n"
     ]
    }
   ],
   "source": [
    "def fibonacci_generator():\n",
    "    a = 0\n",
    "    b = 1\n",
    "    yield 1\n",
    "    while True:\n",
    "        yield a + b\n",
    "        a, b = b, (a + b)\n",
    "        \n",
    "for i, f in enumerate(fibonacci_generator()):\n",
    "    if len(str(f)) >= 1000:\n",
    "        break\n",
    "\n",
    "s = i + 1\n",
    "assert(s == 4782)\n",
    "print(s)"
   ]
  }
 ],
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  "completion_date": "Fri, 5 Sep 2014, 14:57",
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