I'm trying to understand how to calculate the NURBS (non-uniform rational b-spline) basis function(s).

I'm looking at this source on wikipedia: Non-uniform rational B-spline - Wikipedia, the free encyclopedia

It says that the basis function is calculated as:
Ni,n = fi,nNi,n − 1 + gi + 1,nNi + 1,n − 1

But how is it possible that to calculate Ni,n, I need to use the value of Ni,n? It seems like circular logic to me - can anyone please help me understand this?

All I want to know is how to calculate the basis function.

I'd really appreciate any help (p.s. this isn't homework or university work, my hobby is computer graphics).

Cheers to anyone who spent the time reading this.