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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 ...
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.
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 number of a person's father is twice their own number, and the number of a person's mother is twice their own, plus one. For instance, if John Smith is 10, his father is 20, and his mother is 21, and his daughter is 5. In order to readily have the generation stated for a certain person, the Ahnentafel numbering may be preceded by the ...
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The Wedderburn–Etherington numbers may be calculated using the recurrence relation = = = (+) + = beginning with the base case =. [4]In terms of the interpretation of these numbers as counting rooted binary trees with n leaves, the summation in the recurrence counts the different ways of partitioning these leaves into two subsets, and of forming a subtree having each subset as its leaves.
But one can also order them in columns corresponding to the number of moved elements = (sequence A098825 in the OEIS). Each entry in the table below on the left can be factored into two terms given in the table below on the right: the product of a binomial coefficient (given first in red ) and a subfactorial (given second in blue ).
The number of alternative assignments for a given number of workers, taking into account the choices of how many stages to use and how to assign workers to each stage, is an ordered Bell number. [29] As another example, in the computer simulation of origami , the ordered Bell numbers give the number of orderings in which the creases of a crease ...