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In mathematics, integer factorization is the decomposition of a positive integer into a product of integers. Every positive integer greater than 1 is either the product of two or more integer factors greater than 1, in which case it is a composite number, or it is not, in which case it is a prime number.
Karatsuba multiplication of az+b and cz+d (boxed), and 1234 and 567 with z=100. Magenta arrows denote multiplication, amber denotes addition, silver denotes subtraction and cyan denotes left shift. (A), (B) and (C) show recursion with z=10 to obtain intermediate values. The Karatsuba algorithm is a fast multiplication algorithm.
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 .
If a positional numeral system is used, a natural way of multiplying numbers is taught in schools as long multiplication, sometimes called grade-school multiplication, sometimes called the Standard Algorithm: multiply the multiplicand by each digit of the multiplier and then add up all the properly shifted results.
For example, the integers with exactly 12 divisors take the forms , , , and , where , , and are distinct prime numbers; these forms correspond to the multiplicative partitions , , , and respectively. More generally, for each multiplicative partition k = ∏ t i {\displaystyle k=\prod t_{i}} of the integer k {\displaystyle k} , there corresponds ...
Graphs of functions commonly used in the analysis of algorithms, showing the number of operations versus input size for each function. The following tables list the computational complexity of various algorithms for common mathematical operations.
In any case, this algorithm will provide a way to multiply two positive integers, provided is chosen so that < +. Let n = D M {\displaystyle n=DM} be the number of bits in the signals a {\displaystyle a} and b {\displaystyle b} , where D = 2 k {\displaystyle D=2^{k}} is a power of two.
In number theory, a multiplicative function is an arithmetic function f(n) of a positive integer n with the property that f(1) = 1 and = () whenever a and b are coprime.. An arithmetic function f(n) is said to be completely multiplicative (or totally multiplicative) if f(1) = 1 and f(ab) = f(a)f(b) holds for all positive integers a and b, even when they are not coprime.