10

10 is the integer succeeding 9 and preceding 11

Properties
10 is the base in our number system

10 is a semiprime

10 is a brilliant number (product of 2 primes with same number of digits)

10 is the smallest number whose status is unknown whether it is solitary or friendly

10 is the 4th triangular number

10 is the 3rd tetrahedral number

A 10 sided polygon is called a decagon