##sqrt(17)## is not simplifiable and is irrational.
We can calculate rational approximations like:
##sqrt(17) ~~ 268/65 ~~ 4.1231##
Since ##17## is prime it has no square factors so ##sqrt(17)## cannot be simplified.
It is an irrational number a little larger than ##4##.
Since ##17=4^2+1## is in the form ##n^2+1## ##sqrt(17)## has a particularly simple continued fraction expansion:
##sqrt(17) = [4;bar(8)] = 4+1/(8+1/(8+1/(8+1/(8+1/(8+1/(8+…))))))##
You can terminate this continued fraction expansion early to get rational approximations to ##sqrt(17)##.
For example:
##sqrt(17) ~~ [4;88] = 4+1/(8+1/8) = 4+8/65 = 268/65 = 4.1bar(230769)##
Actually:
##sqrt(17) ~~ 4.12310562561766054982##