Friendly numbers are individual numbers that make up part of what is known as a friendly pair. Friendly numbers always come in sets of two, and they are known for having a positive density.
Wolfram's MathWorld explains that any numbers that are not friendly are known as solitary numbers. The Daily Caller discusses the fact that friendly numbers are a concept that was introduced by the common core system in public schools. The common core is a controversial system designed to simplify math, although there has been significant criticism of its ability to achieve that goal. Friendly numbers are used to make a complicated math problem simpler to solve. For example, the Daily Caller explains that a problem in which the student is asked to subtract 270 from 530 could be made simpler by adding 30 to both numbers. Once the simpler problem is solved, the student must undo the adjustments they made to create the friendly numbers. The primary reason for the use of friendly numbers is to make a problem easier to solve in the student's head, but the process has often been cited as causing more confusion and increasing the amount of steps it takes to solve even the most basic problems.