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The first: 4, 8, 9, 16, 25, 27, 32, 36, 49, 64, 81, 100 (sequence A001597 in the OEIS). 1 is sometimes included. A powerful number (also called squareful ) has multiplicity above 1 for all prime factors.
Squares are always congruent to 0, 1, 4, 5, 9, 16 modulo 20. The values repeat with each increase of a by 10. In this example, N is 17 mod 20, so subtracting 17 mod 20 (or adding 3), produces 3, 4, 7, 8, 12, and 19 modulo 20 for these values. It is apparent that only the 4 from this list can be a square.
For example, 3 × 5 is an integer factorization of 15, and (x – 2)(x + 2) is a polynomial factorization of x 2 – 4. Factorization is not usually considered meaningful within number systems possessing division , such as the real or complex numbers , since any x {\displaystyle x} can be trivially written as ( x y ) × ( 1 / y ) {\displaystyle ...
If one of the factors is composite, it can in turn be written as a product of smaller factors, for example 60 = 3 · 20 = 3 · (5 · 4). Continuing this process until every factor is prime is called prime factorization ; the result is always unique up to the order of the factors by the prime factorization theorem .
Name First elements Short description OEIS Mersenne prime exponents : 2, 3, 5, 7, 13, 17, 19, 31, 61, 89, ... Primes p such that 2 p − 1 is prime.: A000043 ...
= 8.4 6 × 10 −5 m/s foot per minute: fpm ≡ 1 ft/min = 5.08 × 10 −3 m/s: foot per second: fps ≡ 1 ft/s = 3.048 × 10 −1 m/s: furlong per fortnight: ≡ furlong/fortnight ≈ 1.663 095 × 10 −4 m/s: inch per hour: iph ≡ 1 in/h = 7.0 5 × 10 −6 m/s inch per minute: ipm ≡ 1 in/min = 4.2 3 × 10 −4 m/s inch per second: ips ≡ ...
If two or more factors of a polynomial are identical, then the polynomial is a multiple of the square of this factor. The multiple factor is also a factor of the polynomial's derivative (with respect to any of the variables, if several). For univariate polynomials, multiple factors are equivalent to multiple roots (over a suitable extension field).
Finding a suitable pair (,) does not guarantee a factorization of , but it implies that is a factor of = (+), and there is a good chance that the prime divisors of are distributed between these two factors, so that calculation of the greatest common divisor of and will give a non-trivial factor of .