A number that shares its prime factors with another.

(number theory) A (nonzero) natural number that is expressible as the product of two (or more) natural numbers other than itself and 1.

plural of Fibonacci number

(physics) A quantum number related to the difference between the numbers of quarks and antiquarks in a system of subatomic particles

(number theory) One of a pair of numbers having the property that the sum of the divisors of each, excluding itself, is equal to the other number.

(mathematics) A number whose decimal representation of its square ends in itself.

(number theory) Any of a series of numbers formed from the sum of the reciprocals of consecutive natural numbers

(physics) The number of neutrons in the nucleus of an atom or isotope. Symbol: N

(mathematics) Any number in a Fibonacci sequence (being the sum of the preceding two numbers)

(mathematics) A number that represents the number of items in a pyramid having a given number of sides and layers