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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.
8128 is the integer following 8127 and preceding 8129.. It is most notable for being a perfect number (its proper divisors 1, 2, 4, 8, 16, 32, 64, 127, 254, 508, 1016, 2032, and 4064 add up to 8128), and one of the earliest numbers to be recognized as such.
Square number 16 as sum of gnomons. In mathematics, a square number or perfect square is an integer that is the square of an integer; [1] in other words, it is the product of some integer with itself. For example, 9 is a square number, since it equals 3 2 and can be written as 3 × 3.
This is due to the Euclid–Euler theorem, partially proved by Euclid and completed by Leonhard Euler: even numbers are perfect if and only if they can be expressed in the form 2 p−1 × (2 p − 1), where 2 p − 1 is a Mersenne prime. In other words, all numbers that fit that expression are perfect, while all even perfect numbers fit that form.
The sum of Euler's totient function φ(x) over the first twenty integers is 128. [4] 128 can be expressed by a combination of its digits with mathematical operators, thus 128 = 2 8 − 1, making it a Friedman number in base 10. [5] A hepteract has 128 vertices. 128 is the only 3-digit number that is a 7th power (2 7).
But here, the context is the set of integers. If you consider that you should not have an implicit context, then the term perfect square is also ambiguous, because it is also used for non-integers, like here, where 102.01 is regarded as a perfect square because (10.1)² = 102.01 exactly. See also the footnote saying: "Some authors also call ...
The Alzheimer's Association released a list of gift recommendations for individuals with the disease at every stage of dementia. Experts offer insights on how to navigate the holiday amid dementia.
Consequently, a square number is also triangular if and only if + is square, that is, there are numbers and such that =. This is an instance of the Pell equation x 2 − n y 2 = 1 {\displaystyle x^{2}-ny^{2}=1} with n = 8 {\displaystyle n=8} .