Also, it's easily provable (using pumping lemma) that the language: { 1^n | n is a prime number } is non-regular, so no "regular expression" (referring to stric

Also, it's easily provable (using pumping lemma) that the language: { 1^n | n is a prime number } is non-regular, so no "regular expression" (referring to strict mathematical definition here) can express it.