Obviously this suitability test can be stretched into something
absurd,
e.g.:

input:

<number-of-primes>6<number-of-primes>

output:

<primes>1,2,3,5,7,11</primes>

Using XLST to do that computation would not be a great idea :-)...

Why do you think so?

See the XSLT solution of the Google's "Find the first sequence of 10
consecutive digits of e, which is a prime number"

at:
    http://www.xsltblog.com/archives/code/code_of_the_day/index.html

Cheers,
-ml-