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    "# Practical course 3\n",
    "\n",
    "## Task 1\n",
    "\n",
    "Finally, we work with lists. Lists are similiar to strings but can contain various data types. Therefore you should be already quite familiar with it.\n",
    "\n",
    "1. Use a _loop_ to ask the user on the console three times for names of friends and store them in a list.\n",
    "2. Go through the list in a _loop_ and output the following text for each entry: ``Friend N: NAME``. Replace ``N`` with a sequence number (starting with 1) and ``NAME`` with the name from the list. (Hint: ``enumerate``)\n",
    "3. Remove the last entry from the list.\n",
    "4. Output the length of the list."
   ]
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    "## Task 2\n",
    "\n",
    "Write the following basic functions:\n",
    "\n",
    "1. Write the function ``add``. This function takes two numbers as arguments and returns there sum"
   ]
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    "2. Write the function ``is_even``. This function accepts a number as a parameter and returns a boolean expression (True when even, False when odd)"
   ]
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    "3. Implement ``is_odd``. Hint: Do not write it from scratch. Reuse ``is_even`` instead."
   ]
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    "4. Write the function ``even_or_odd``.\n",
    "\n",
    "This function accepts a list of numbers as a parameter.\n",
    "\n",
    "The function counts how many numbers in the list are even or odd and returns the following tuple: ``(amount of even numbers, amount of odd numbers)``"
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    "## Task 3\n",
    "\n",
    "For calculating the sum of all integers from 0 to n the following formula can be used:\n",
    "\n",
    "$$0 + 1 + 2 + 3 + 4 + \\dotsb + n = \\sum_{k=0}^n k = \\frac{n(n+1)}{2} = \\frac{n^2+n}{2}$$\n",
    "\n",
    "In German this is called the \"Sum formula of Gauss\". This formula does not seem to have any fancy name in English.\n",
    "\n",
    "$$\\sum_{k=0}^n k$$ is the _recursive_ formula because the result of the next value is based on the previous one.\n",
    "\n",
    "$$\\frac{n(n+1)}{2} = \\frac{n^2+n}{2}$$ are the _explicit_ formulas because they calculate a concreate, single value of the sequence.\n",
    "\n",
    "1. Read in the Python documentation about the built-in function ``sum``.\n",
    "2. Write the function ``sum_explicit`` which accepts ``n`` (see formula above) as an argument and calculates the sum using the _explicit_ formula. (do not use built-in ``sum``)\n",
    "3. Write the function ``sum_loop`` which accepts ``n`` (see formula above) as an argument and calculates the sum using the _recursive_ formula. (for-loop, do not use built-in ``sum``)"
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   "source": [
    "## Task 4"
   ]
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    "A prime number is a natural number greater than 1 that is not a product of two smaller natural numbers.\n",
    "\n",
    "Write the function ``is_prime`` that decides whether a passed number is prime (``True``) or not (``False``)"
   ]
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