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It states that an even number is perfect if and only if it has the form 2 p−1 (2 p − 1), where 2 p − 1 is a prime number. The theorem is named after mathematicians Euclid and Leonhard Euler, who respectively proved the "if" and "only if" aspects of the theorem. It has been conjectured that there are infinitely many Mersenne primes.
The parity function maps a number to the number of 1's in its binary representation, modulo 2, so its value is zero for evil numbers and one for odious numbers. The Thue–Morse sequence , an infinite sequence of 0's and 1's, has a 0 in position i when i is evil, and a 1 in that position when i is odious.
The standard definition of "even number" can be used to directly prove that zero is even. A number is called "even" if it is an integer multiple of 2. As an example, the reason that 10 is even is that it equals 5 × 2.
As an illustration of this, the parity cycle (1 1 0 0 1 1 0 0) and its sub-cycle (1 1 0 0) are associated to the same fraction 5 / 7 when reduced to lowest terms. In this context, assuming the validity of the Collatz conjecture implies that (1 0) and (0 1) are the only parity cycles generated by positive whole numbers (1 and 2 ...
If n > 1, then there are just as many even permutations in S n as there are odd ones; [3] consequently, A n contains n!/2 permutations. (The reason is that if σ is even then (1 2)σ is odd, and if σ is odd then (1 2)σ is even, and these two maps are inverse to each other.) [3] A cycle is even if and only if its length is odd. This follows ...
Euclid offered a proof published in his work Elements (Book IX, Proposition 20), [1] which is paraphrased here. [2] Consider any finite list of prime numbers p 1, p 2, ..., p n. It will be shown that there exists at least one additional prime number not included in this list. Let P be the product of all the prime numbers in the list: P = p 1 p ...
where p 1 < p 2 < ... < p k are primes and the n i are positive integers. This representation is commonly extended to all positive integers, including 1, by the convention that the empty product is equal to 1 (the empty product corresponds to k = 0). This representation is called the canonical representation [10] of n, or the standard form [11 ...
One proof is to note that φ(d) is also equal to the number of possible generators of the cyclic group C d ; specifically, if C d = g with g d = 1, then g k is a generator for every k coprime to d. Since every element of C n generates a cyclic subgroup, and each subgroup C d ⊆ C n is generated by precisely φ(d) elements of C n, the formula ...