/ Dictionary / Index M Mersenne number: Meaning and Definition of Find definitions for: Mersenne' num"ber Pronunciation: [key] a number of the form, 2 −1, where p is a prime number. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Mersenne Mersey Related Content Daily Word Quiz: winsome Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language