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Doc/library/math.integer.rst
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Ned Batchelder
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:mod:`!math.integer` --- integer-specific mathematics functions
===============================================================

.. module:: math.integer
   :synopsis: Integer-specific mathematics functions.

.. versionadded:: 3.15

--------------

This module provides access to the mathematical functions defined for integer arguments.
These functions accept integers and objects that implement the
:meth:`~object.__index__` method which is used to convert the object to an integer
number.

The following functions are provided by this module.  All return values are
computed exactly and are integers.


.. function:: comb(n, k, /)

   Return the number of ways to choose *k* items from *n* items without repetition
   and without order.

   Evaluates to ``n! / (k! * (n - k)!)`` when ``k <= n`` and evaluates
   to zero when ``k > n``.

   Also called the binomial coefficient because it is equivalent
   to the coefficient of k-th term in polynomial expansion of
   ``(1 + x)ⁿ``.

   Raises :exc:`ValueError` if either of the arguments are negative.


.. function:: factorial(n, /)

   Return factorial of the nonnegative integer *n*.


.. function:: gcd(*integers)

   Return the greatest common divisor of the specified integer arguments.
   If any of the arguments is nonzero, then the returned value is the largest
   positive integer that is a divisor of all arguments.  If all arguments
   are zero, then the returned value is ``0``.  ``gcd()`` without arguments
   returns ``0``.


.. function:: isqrt(n, /)

   Return the integer square root of the nonnegative integer *n*. This is the
   floor of the exact square root of *n*, or equivalently the greatest integer
   *a* such that *a*\ ² |nbsp| ≤ |nbsp| *n*.

   For some applications, it may be more convenient to have the least integer
   *a* such that *n* |nbsp| ≤ |nbsp| *a*\ ², or in other words the ceiling of
   the exact square root of *n*. For positive *n*, this can be computed using
   ``a = 1 + isqrt(n - 1)``.


   .. |nbsp| unicode:: 0xA0
      :trim:


.. function:: lcm(*integers)

   Return the least common multiple of the specified integer arguments.
   If all arguments are nonzero, then the returned value is the smallest
   positive integer that is a multiple of all arguments.  If any of the arguments
   is zero, then the returned value is ``0``.  ``lcm()`` without arguments
   returns ``1``.


.. function:: perm(n, k=None, /)

   Return the number of ways to choose *k* items from *n* items
   without repetition and with order.

   Evaluates to ``n! / (n - k)!`` when ``k <= n`` and evaluates
   to zero when ``k > n``.

   If *k* is not specified or is ``None``, then *k* defaults to *n*
   and the function returns ``n!``.

   Raises :exc:`ValueError` if either of the arguments are negative.