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By the lemma above, since s is odd and its cube is equal to a number of the form 3w 2 + v 2, it too can be expressed in terms of smaller coprime numbers, e and f. s = e 2 + 3f 2. A short calculation shows that v = e(e 2 − 9f 2) w = 3f(e 2 − f 2) Thus, e is odd and f is even, because v is odd. The expression for 18w then becomes
Equivalent statement 2: x n + y n = z n, where integer n ≥ 3, has no non-trivial solutions x, y, z ∈ Q. This is because the exponents of x, y, and z are equal (to n), so if there is a solution in Q, then it can be multiplied through by an appropriate common denominator to get a solution in Z, and hence in N.
Euler proved that every factor of F n must have the form k 2 n+1 + 1 (later improved to k 2 n+2 + 1 by Lucas) for n ≥ 2. That 641 is a factor of F 5 can be deduced from the equalities 641 = 2 7 × 5 + 1 and 641 = 2 4 + 5 4 .
For example, if a = 2 and p = 7, then 2 7 = 128, and 128 − 2 = 126 = 7 × 18 is an integer multiple of 7. If a is not divisible by p, that is, if a is coprime to p, then Fermat's little theorem is equivalent to the statement that a p − 1 − 1 is an integer multiple of p, or in symbols: [1] [2] ().
On the other hand, the primes 3, 7, 11, 19, 23 and 31 are all congruent to 3 modulo 4, and none of them can be expressed as the sum of two squares. This is the easier part of the theorem, and follows immediately from the observation that all squares are congruent to 0 (if number squared is even) or 1 (if number squared is odd) modulo 4.
The first 3 powers of 2 with all but last digit odd is 2 4 = 16, 2 5 = 32 and 2 9 = 512. The next such power of 2 of form 2 n should have n of at least 6 digits. The only powers of 2 with all digits distinct are 2 0 = 1 to 2 15 = 32 768 , 2 20 = 1 048 576 and 2 29 = 536 870 912 .
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Two problems where the factor theorem is commonly applied are those of factoring a polynomial and finding the roots of a polynomial equation; it is a direct consequence of the theorem that these problems are essentially equivalent.