The problem of the representation of integers is an old problem. Waring’s
problem establish that every nonnegative integer is the sum of a fixed number
of nonnegative k-th powers. This fixed number depends of k. For example,
all nonnegative integer is the sum of four nonnegative squares (Lagrange’s
Theorem). The Waring’s problem was solved by Hilbert. This is a very difficult
problem. The history of the Waring’s problem is given in [3].
Goldbach conjectured that every even positive integer is the sum of two
prime numbers. The Goldbach’s conjecture is an open problem.
It is also natural to consider the problem of the representation of an integer
as the sum of a fixed number of members of the set