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Quasi-sociable numbers or reduced sociable numbers are numbers whose aliquot sums minus one form a cyclic sequence that begins and ends with the same number. They are generalizations of the concepts of betrothed numbers and quasiperfect numbers. The first quasi-sociable sequences, or quasi-sociable chains, were discovered by Mitchell Dickerman ...
In number theory, an evil number is a non-negative integer that has an even number of 1s in its binary expansion. [1] These numbers give the positions of the zero values in the Thue–Morse sequence, and for this reason they have also been called the Thue–Morse set. [2] Non-negative integers that are not evil are called odious numbers.
For a perfect number n the sum of all its divisors is equal to 2n. For an almost perfect number n the sum of all its divisors is equal to 2n - 1. Numbers n exist whose sum of factors = 2n + 2. They are of form 2^(n - 1) * (2^n - 3) where 2^n - 3 is a prime. The only exception known till yet is 650 = 2 * 5^2 * 13.
In mathematics, the amicable numbers are two different natural numbers related in such a way that the sum of the proper divisors of each is equal to the other number. That is, s ( a )= b and s ( b )= a , where s ( n )=σ( n )- n is equal to the sum of positive divisors of n except n itself (see also divisor function ).
The period of the sequence, or order of the set of sociable numbers, is the number of numbers in this cycle. If the period of the sequence is 1, the number is a sociable number of order 1, or a perfect number—for example, the proper divisors of 6 are 1, 2, and 3, whose sum is again 6. A pair of amicable numbers is a set of sociable numbers of ...
In number theory, a narcissistic number [1] [2] (also known as a pluperfect digital invariant (PPDI), [3] an Armstrong number [4] (after Michael F. Armstrong) [5] or a plus perfect number) [6] in a given number base is a number that is the sum of its own digits each raised to the power of the number of digits.
3. Digital Watches . Lars Fortuin/istockphoto ... these pocket calculators were the go-to tool for anything from simple calculations to more advanced math equations. Though early models were ...
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