Sentence:  A <WSD>highly composite number</WSD>, then, was in Hardy's phrase "as unlike a prime as a number can be." Ramanujan had explored their properties for some time; in the earliest pages of his second notebook he'd listed about a hundred <WSD>highly composite numbers</WSD>−the first few are 2, 4, 6, 12, 24, 36, 48, 60, 120−searching for patterns. He found them. 
Meaning of the word marked with <WSD> tags:  A positive integer that has more divisors than any smaller positive integer.