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Demonstration, with Cuisenaire rods, of the abundance of the number 12. In number theory, an abundant number or excessive number is a positive integer for which the sum of its proper divisors is greater than the number.
Definition. An integer is divisible by a nonzero integer if there exists an integer such that This is written as. This may be read as that divides is a divisor of is a factor of or is a multiple of If does not divide then the notation is [ 2][ 3] There are two conventions, distinguished by whether is permitted to be zero:
By definition, a perfect number is a fixed point of the restricted divisor function s(n) = σ(n) − n, and the aliquot sequence associated with a perfect number is a constant sequence. All perfect numbers are also -perfect numbers, or Granville numbers . A semiperfect number is a natural number that is equal to the sum of all or some of its ...
Divisor function. In mathematics, and specifically in number theory, a divisor function is an arithmetic function related to the divisors of an integer. When referred to as the divisor function, it counts the number of divisors of an integer (including 1 and the number itself). It appears in a number of remarkable identities, including ...
Comoving distance and proper distance. Comoving distance is the distance between two points measured along a path defined at the present cosmological time. For objects moving with the Hubble flow, it is deemed to remain constant in time. The comoving distance from an observer to a distant object (e.g. galaxy) can be computed by the following ...
Q. factor. A damped oscillation. A low Q factor – about 5 here – means the oscillation dies out rapidly. In physics and engineering, the quality factor or Q factor is a dimensionless parameter that describes how underdamped an oscillator or resonator is. It is defined as the ratio of the initial energy stored in the resonator to the energy ...
A prime number (or a prime) is a natural number greater than 1 that is not a product of two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number. For example, 5 is prime because the only ways of writing it as a product, 1 × 5 or 5 × 1, involve 5 itself. However, 4 is composite because it is a ...
Definition. There are two definitions for the factor of safety (FoS): The ratio of a structure's absolute strength (structural capability) to actual applied load; this is a measure of the reliability of a particular design. This is a calculated value, and is sometimes referred to, for the sake of clarity, as a realized factor of safety.