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jmc

number theory senior

Problem

One of Euler's conjectures was disproved in the 1960s by three American mathematicians when they showed there was a positive integer such that . Find the value of .
Solution
Note that is even, since the consists of two odd and two even numbers. By Fermat's Little Theorem, we know is congruent to modulo 5. Hence, Continuing, we examine the equation modulo 3, Thus, is divisible by three and leaves a remainder of four when divided by 5. It's obvious that , so the only possibilities are or . It quickly becomes apparent that 174 is much too large, so must be .
Final answer
144