Search results
Results from the WOW.Com Content Network
To test the divisibility of a number by a power of 2 or a power of 5 (2 n or 5 n, in which n is a positive integer), one only need to look at the last n digits of that number. To test divisibility by any number expressed as the product of prime factors , we can separately test for divisibility by each prime to its appropriate power.
But Fermat numbers grow so rapidly that only a handful of them can be tested in a reasonable amount of time and space. There are some tests for numbers of the form k 2 m + 1, such as factors of Fermat numbers, for primality. Proth's theorem (1878). Let N = k 2 m + 1 with odd k < 2 m. If there is an integer a such that
Using fast algorithms for modular exponentiation and multiprecision multiplication, the running time of this algorithm is O(k log 2 n log log n) = Õ(k log 2 n), where k is the number of times we test a random a, and n is the value we want to test for primality; see Miller–Rabin primality test for details.
1 Divisibility. 2 Fractions. 3 Modular arithmetic. 4 Arithmetic functions. ... Lucas–Lehmer test for Mersenne numbers; AKS primality test; Integer factorization
Since 2 divides , +, and +, and 3 divides and +, the only possible remainders mod 6 for a prime greater than 3 are 1 and 5. So, a more efficient primality test for is to test whether is divisible by 2 or 3, then to check through all numbers of the form + and + which are .
A prime number is a natural number that has exactly two distinct natural number divisors: the number 1 and itself. To find all the prime numbers less than or equal to a given integer n by Eratosthenes' method: Create a list of consecutive integers from 2 through n: (2, 3, 4, ..., n). Initially, let p equal 2, the smallest prime number.
In fact, if and are coprime, then this is a strong divisibility sequence. The Fibonacci numbers F n form a strong divisibility sequence. More generally, any Lucas sequence of the first kind U n (P,Q) is a divisibility sequence. Moreover, it is a strong divisibility sequence when gcd(P,Q) = 1. Elliptic divisibility sequences are another class of ...
6: an even number that passes the divisibility test for 3. 7: sum of all the digits is a multiple of 7. 5: successive subtraction of final two digits from all the other digits yields a multiple of 5. 12: an even number that passes the divisibility test for 5. Base 11 (a prime base, for comparison): 2: sum of all the digits is a multiple of 2.