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Dixon's method replaces the condition "is the square of an integer" with the much weaker one "has only small prime factors"; for example, there are 292 squares smaller than 84923; 662 numbers smaller than 84923 whose prime factors are only 2,3,5 or 7; and 4767 whose prime factors are all less than 30. (Such numbers are called B-smooth with ...
The CRT says that this is the same as p ≡ 1 (mod 840), and Dirichlet's theorem says there are an infinite number of primes of this form. 2521 is the smallest, and indeed 1 2 ≡ 1, 1046 2 ≡ 2, 123 2 ≡ 3, 2 2 ≡ 4, 643 2 ≡ 5, 87 2 ≡ 6, 668 2 ≡ 7, 429 2 ≡ 8, 3 2 ≡ 9, and 529 2 ≡ 10 (mod 2521).
The former are ≡ ±1 (mod 12) and the latter are all ≡ ±5 (mod 12). −3 is in rows 7, 13, 19, 31, 37, and 43 but not in rows 5, 11, 17, 23, 29, 41, or 47. The former are ≡ 1 (mod 3) and the latter ≡ 2 (mod 3). Since the only residue (mod 3) is 1, we see that −3 is a quadratic residue modulo every prime which is a residue modulo 3.
Example 1: Finding primes for which a is a residue. Let a = 17. For which primes p is 17 a quadratic residue? We can test prime p's manually given the formula above. In one case, testing p = 3, we have 17 (3 − 1)/2 = 17 1 ≡ 2 ≡ −1 (mod 3), therefore 17 is not a quadratic residue modulo 3.
We do this in a vector format; for example, the prime-power factorization of 504 is 2 3 3 2 5 0 7 1, it is therefore represented by the exponent vector (3,2,0,1). Multiplying two integers then corresponds to adding their exponent vectors. A number is a square when its exponent vector is even in every coordinate.
In mathematics, a square-free integer (or squarefree integer) is an integer which is divisible by no square number other than 1. That is, its prime factorization has exactly one factor for each prime that appears in it. For example, 10 = 2 ⋅ 5 is square-free, but 18 = 2 ⋅ 3 ⋅ 3 is not, because 18 is divisible by 9 = 3 2. The smallest ...
Since a prime number has factors of only 1 and itself, and since m = 2 is the only non-zero value of m to give a factor of 1 on the right side of the equation above, it follows that 3 is the only prime number one less than a square (3 = 2 2 − 1). More generally, the difference of the squares of two numbers is the product of their sum and ...
Positive numbers: Real numbers that are greater than zero. Negative numbers: Real numbers that are less than zero. Because zero itself has no sign, neither the positive numbers nor the negative numbers include zero. When zero is a possibility, the following terms are often used: Non-negative numbers: Real numbers that are greater than or equal ...