A Number Behind Each Variable?

Let's take a random variable a (in math). We can say either it's monomial, or polynomial, i.e. either it is a number (or a group of it), or another variable (or a group of it). 

But here's a question: is it true that behind each variable in Math there is a number or a group of numbers?
(The same question written symbolically):

(∀y)(∃x){[(Vy≡"y is variable") & (V₁y≡Vy ∨ V₂y≡Vy ∨ ... ∨ V_ny≡Vy)] ⊃ [(Nx≡"n is number") & (N₁x≡Vy ∨ N₂x≡Vy ∨ ... ∨ N_kx≡Vy)]}

(another way):

(∀a)(∃x)(a≡x ⊃ x ∈ ℔)       (where "℔" is a symbol of any number; i.e. it might belong to rational, or natural, etc.)

Or is it possible that some variables don't have numbers behind them, and if there are, what are these variables?