Today is 5 day of the year.
5 is prime.
5 is a safe prime.
5 = 2 + 3, i.e. the sum of the first two primes.
5 is Fibonacci number.
5 is an untouchable number and conjectured to be the only odd one.
There are 5 platonic solids.
5 is the fourth Pell number.
The series of fractions formed by taking a Pell number as the denominator and the sum of the Pell number and its predecessor, gets arbitrarily close to the square root of two.