What kind representations exist $\forall n\in \mathbb N$?
For example, each natural number $n$ can be expressed as:
$1)$ A sum of four squares (Lagrange)
$2)$ A sum of three triangular numbers (Gauss)
$3)$ A sum of Fibonacci numbers (Zeckendorfs theorem)
$4)$ A product of primes (Fundamental theorem of Number Theory)
$5)$ Factoradic digits
$6)$ Sum of "digits" in the usual sense
Are there more representations which work for every natural number?