bpo-39479:Add math.lcm() function: Least Common Multiple (#18547)

* Update math.rst

* Update math.rst

* updated whats new

* Update test_math.py

* Update mathmodule.c

* Update mathmodule.c.h

* Update ACKS

* 📜🤖 Added by blurb_it.

* Update 3.9.rst

* Update 2020-02-18-12-37-16.bpo-39479.j3UcCq.rst

* Update math.rst

* Update 2020-02-18-12-37-16.bpo-39479.j3UcCq.rst

* Update test_math.py

* Update ACKS

* Update mathmodule.c.h

* Update mathmodule.c

* Update mathmodule.c.h

* Update mathmodule.c.h

Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
diff --git a/Doc/library/math.rst b/Doc/library/math.rst
index c4c1800..d8ac352 100644
--- a/Doc/library/math.rst
+++ b/Doc/library/math.rst
@@ -136,6 +136,15 @@
    .. versionadded:: 3.5
 
 
+.. function:: lcm(a, b)
+
+   Return the least common multiple of integers *a* and *b*.  The value of
+   ``lcm(a, b)`` is the smallest nonnegative integer that is a multiple of
+   both *a* and *b*.  If either *a* or *b* is zero then ``lcm(a, b)`` is zero.
+
+   .. versionadded:: 3.9
+
+
 .. function:: isclose(a, b, *, rel_tol=1e-09, abs_tol=0.0)
 
    Return ``True`` if the values *a* and *b* are close to each other and