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A simplified version of the LLL factorization algorithm is as follows: calculate a complex (or p-adic) root α of the polynomial () to high precision, then use the Lenstra–Lenstra–Lovász lattice basis reduction algorithm to find an approximate linear relation between 1, α, α 2, α 3, . . . with integer coefficients, which might be an ...
Suppose N has more than two prime factors. That procedure first finds the factorization with the least values of a and b . That is, a + b {\displaystyle a+b} is the smallest factor ≥ the square-root of N , and so a − b = N / ( a + b ) {\displaystyle a-b=N/(a+b)} is the largest factor ≤ root- N .
Pollard's p − 1 algorithm is a number theoretic integer factorization algorithm, invented by John Pollard in 1974. It is a special-purpose algorithm, meaning that it is only suitable for integers with specific types of factors; it is the simplest example of an algebraic-group factorisation algorithm .
Start with division by 2: the number is even, and n = 2 · 693. Continue with 693, and 2 as a first divisor candidate. 693 is odd (2 is not a divisor), but is a multiple of 3: one has 693 = 3 · 231 and n = 2 · 3 · 231. Continue with 231, and 3 as a first divisor candidate. 231 is also a multiple of 3: one has 231 = 3 · 77, and thus n = 2 ...
Let's choose the elliptic curve y 2 = x 3 + 5x – 5, with the point P = (1, 1) on it, and let's try to compute (10!)P. The slope of the tangent line at some point A=(x, y) is s = (3x 2 + 5)/(2y) (mod n). Using s we can compute 2A. If the value of s is of the form a/b where b > 1 and gcd(a,b) = 1, we have to find the modular inverse of b.
To factorize a small integer n using mental or pen-and-paper arithmetic, the simplest method is trial division: checking if the number is divisible by prime numbers 2, 3, 5, and so on, up to the square root of n. For larger numbers, especially when using a computer, various more sophisticated factorization algorithms are more efficient.
When using such algorithms to factor a large number n, it is necessary to search for smooth numbers (i.e. numbers with small prime factors) of order n 1/2. The size of these values is exponential in the size of n (see below). The general number field sieve, on the other hand, manages to search for smooth numbers that are subexponential in the ...
For more factorization algorithms see e.g. Knuth's book The Art of Computer Programming volume 2. Algorithm Cantor–Zassenhaus algorithm. Input: A finite field F q of odd order q. A monic square free polynomial f in F q [x] of degree n = rd, which has r ≥ 2 irreducible factors each of degree d Output: The set of monic irreducible factors of f.