The Frobenius number is the largest value for which the Frobenius equation
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has no solution, where the are positive integers, is an integer, and the solutions are nonnegative integer. As an example, if the values are 4 and 9, then 23 is the largest unsolvable number. Similarly, the largest number that is not a McNugget number (a number obtainable by adding multiples of 6, 9, and 20) is 43.
Finding the Frobenius number of a given problem is known as the coin problem.
Computation of the Frobenius number is implemented in the Wolfram Language as FrobeniusNumber[a1, ..., an].
Sylvester (1884) showed
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