The core of the program for first year students is a single course in number theory.

He spent the rest of his life studying number theory.

He also contributed to many other areas of number theory.

In the main, he worked on number theory and infinite series.

Most of his work was about number theory and astronomy.

Such a view is no longer applicable to number theory.

And in fact you can imagine lots of number theory has gone into this.

There are thus some problems in number theory that will never be solved.

I guess number theory is the only thing I'm really good at.

He is known primarily for his contributions to number theory.