Chicken McNugget Theorem
The Chicken McNugget Theorem states that for any two relatively prime positive integers 
, the greatest integer that cannot be written in the form 
for nonnegative integers 
is 
.
Proof
Consider the integers 
. Let 
. Note that since 
and 
are relatively prime, 
is a Complete residue system in modulo .
Lemma:
For any given residue class 
, call 
the member of in this class. All members greater than or equal to can be written in the form 
while all members less than cannot for nonnegative 
.
Proof:
Each member of the residue class can be written as
for an integer 
. Since is in the form 
, this can be rewritten as .
Nonnegative values of correspond to members greater than or equal to . Negative values of correspond to members less than . Thus the lemma is proven.
The largest member of is 
, so the largest unattainable score 
is in the same residue class as .
The largest member of this residue class less than is 
and the proof is complete.
See Also
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