2305843009213693951

This number is a prime.

                                                        230584300 9213693951

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Wonder Book of Strange Facts (Ripley's Believe It or Not, Inc., 1957, p. 100) states that this (the 9th Mersenne prime) is the number of ways to make change for a five-dollar bill using pennies, nickels, dimes, quarters, half-dollar, and dollar coins. The correct answer is 98411, making this one of the largest prime errors ever found. [Rupinski]