[R] Looking for package to solve for exponent using newton's method

[Ken Takagi]

Hi,
I'm looking for an R function/package that will let me solve problems of the
type:

13 = 2^x + 3^x.

The answer to this example is x = 2, but I'm looking for solutions when x
isn't so easily determined. Looking around, it seems that there is no
algebraic solution for x, unless I'm mistaken.  Does anyone know a good
package to solve these types of problems? Are there built in functions to do
this?

Thanks!