S4E22. 二分之一的阶乘是多少？伽马函数的诞生

<p style="color:#333333;font-weight:normal;font-size:16px;line-height:30px;font-family:Helvetica,Arial,sans-serif;hyphens:auto;text-align:justify;" data-flag="normal">斯特林公式：</p><p style="color:#333333;font-weight:normal;font-size:16px;line-height:30px;font-family:Helvetica,Arial,sans-serif;hyphens:auto;text-align:justify;" data-flag="normal"><img data-key="0" src="http://imagev2.xmcdn.com/storages/5004-audiofreehighqps/D0/A9/GKwRIasINzdlAAD2lQIb7-7E.png!op_type=4&amp;device_type=ios&amp;upload_type=attachment&amp;name=mobile_large" alt="" data-origin="http://imagev2.xmcdn.com/storages/5004-audiofreehighqps/D0/A9/GKwRIasINzdlAAD2lQIb7-7E.png?op_type=0" data-large="http://imagev2.xmcdn.com/storages/5004-audiofreehighqps/D0/A9/GKwRIasINzdlAAD2lQIb7-7E.png!op_type=4&amp;device_type=ios&amp;upload_type=attachment&amp;name=mobile_large" data-large-width="750" data-large-height="192.19308700834327" data-preview="http://imagev2.xmcdn.com/storages/5004-audiofreehighqps/D0/A9/GKwRIasINzdlAAD2lQI...