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

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

(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.

(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

(physics) A quantum number related to the difference between the number of leptons and antileptons in a system

(mathematics) Any positive integer having the property that all smaller integers can be represented as sums of distinct divisors of it

(mathematics) Any integer that is the sum of n natural numbers from 1 to n.

plural of figurate number