Sentence:  Some poems, echoing the purpose of early poetic treatises on scientific principles, attempt to elucidate the mathematical concepts that underlie prime numbers. Others play with <WSD>primes'</WSD> cultural associations. Still others derive their structure from mathematical patterns involving <WSD>primes</WSD>. 
Meaning of the word marked with <WSD> tags:  A prime element of a mathematical structure, particularly a prime number.