Search results
Results from the WOW.Com Content Network
In number theory, a perfect number is a positive integer that is equal to the sum of its positive proper divisors, that is, divisors excluding the number itself. For instance, 6 has proper divisors 1, 2 and 3, and 1 + 2 + 3 = 6, so 6 is a perfect number. The next perfect number is 28, since 1 + 2 + 4 + 7 + 14 = 28.
Perfect numbers are natural numbers that equal the sum of their positive proper divisors, which are divisors excluding the number itself. So, 6 is a perfect number because the proper divisors of 6 are 1, 2, and 3, and 1 + 2 + 3 = 6. [2] [4] Euclid proved c. 300 BCE that every prime expressed as M p = 2 p − 1 has a corresponding perfect number ...
The Euclid–Euler theorem states that an even natural number is perfect if and only if it has the form 2 p−1 M p, where M p is a Mersenne prime. [1] The perfect number 6 comes from p = 2 in this way, as 2 2−1 M 2 = 2 × 3 = 6, and the Mersenne prime 7 corresponds in the same way to the perfect number 28.
A perfect totient number is an integer that is equal to the sum of its iterated totients. That is, we apply the totient function to a number n, apply it again to the resulting totient, and so on, until the number 1 is reached, and add together the resulting sequence of numbers; if the sum equals n, then n is a perfect totient number.
Alternating triangular numbers (1, 6, 15, 28, ...) are also hexagonal numbers. Every even perfect number is triangular (as well as hexagonal), given by the formula = (+) = where M p is a Mersenne prime. No odd perfect numbers are known; hence, all known perfect numbers are triangular.
A semiperfect number that is not divisible by any smaller semiperfect number is called primitive. Every number of the form 2 m p for a natural number m and an odd prime number p such that p < 2 m+1 is also semiperfect. In particular, every number of the form 2 m (2 m+1 − 1) is semiperfect, and indeed perfect if 2 m+1 − 1 is a Mersenne prime.
Skip to main content. Sign in
Consecutive Fibonacci numbers can also be used to obtain a similar formula for the golden ratio, here by infinite summation: = | + | =. In particular, the powers of φ {\displaystyle \varphi } themselves round to Lucas numbers (in order, except for the first two powers, φ 0 {\displaystyle \textstyle \varphi ^{0}} and φ ...