What do these numbers represent in this schematic diagram?
Tactile switches usually have four pins, with pin pairs already connected to each other. Very often you'll see that the switch closes contact between the pins on a particular side.

Since pin numbering is typically done on alternating sides, but the contact is done between adjacent pins, you can have pairs [1,4] and [2,3] electrically connected.

Here is an excerpt from a common tactile switch datasheet (C&amp;K PTS645):



The schematic (top right corner) shows a slightly different arrangement where the pairs are [1,2] and [3,4].

You can use a switch with either arrangement, just be sure you know which pins are electrically "normally closed" and which are "normally open" by examining the datasheet before you solder.