5479

This number is a prime.

The average of the smallest (1009) and largest (9949) 4-digit primes featured in the book "Prime Curios!: The Dictionary of Prime Number Trivia" by Chris K. Caldwell and G. L. Honaker, Jr., 2009. [Green]

The sum of all multidigit composite repdigit numbers less than a thousand, i.e., 22+33+44+55+66+77+88+99+111+222+333+444+555+666+777+888+999. [Loungrides]

The largest prime factor of 10958 which is on YouTube as "The 10958 Problem". [Homewood]

There are 5479 days in fifteen years. [Giglord]

The total number of bipartite graphs with ten vertices. [Gudipati]