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All integers are either even or odd. A square has even multiplicity for all prime factors (it is of the form a 2 for some a). The first: 1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144 (sequence A000290 in the OEIS). A cube has all multiplicities divisible by 3 (it is of the form a 3 for some a).
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.
If none of its prime factors are repeated, it is called squarefree. (All prime numbers and 1 are squarefree.) For example, 72 = 2 3 × 3 2, all the prime factors are repeated, so 72 is a powerful number. 42 = 2 × 3 × 7, none of the prime factors are repeated, so 42 is squarefree. Euler diagram of numbers under 100:
Primes that are not the sum of a smaller prime and twice the square of a nonzero integer. 2, 3, 17, 137, 227, 977, 1187, 1493 (OEIS: A042978) As of 2011, these are the only known Stern primes, and possibly the only existing.
Divisor. In mathematics, a divisor of an integer also called a factor of is an integer that may be multiplied by some integer to produce [1] In this case, one also says that is a multiple of An integer is divisible or evenly divisible by another integer if is a divisor of ; this implies dividing by leaves no remainder.
A Gaussian integer is either the zero, one of the four units (±1, ± i), a Gaussian prime or composite. The article is a table of Gaussian Integersx + iy followed either by an explicit factorization or followed by the label (p) if the integer is a Gaussian prime. The factorizations take the form of an optional unit multiplied by integer powers ...
The smallest abundant number not divisible by 2 or by 3 is 5391411025 whose distinct prime factors are 5, 7, 11, 13, 17, 19, 23, and 29 (sequence A047802 in the OEIS). An algorithm given by Iannucci in 2005 shows how to find the smallest abundant number not divisible by the first k primes . [ 1 ]
When such a divisor is found, the repeated application of this algorithm to the factors q and n / q gives eventually the complete factorization of n. [1] For finding a divisor q of n, if any, it suffices to test all values of q such that 1 < q and q 2 ≤ n. In fact, if r is a divisor of n such that r 2 > n, then q = n / r is a divisor of n ...