Sylvester's Postage Stamp Problem
What is the greatest positive integer such that the Diophantine equation has no solution in non-negative integers? If and are relatively prime numbers, the equation has a solution in integers for any integer and has a solution in non-negative integers for any integer greater than .
J. J. Sylvester (1814–1897) posed the problem of finding the largest number that cannot be made up of some combination of 5p and 17p stamps.
 D. Wells, The Penguin Book of Curious and Interesting Puzzles, New York: Penguin Books, 1993 p. 64.