(idiomatic) A person who holds a position in an organization that corresponds to that held by another person in another organization; a counterpart

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

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

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

For a given set of coprime positive integers, the greatest integer that cannot be expressed as a linear combination (with nonnegative integer coefficients) of its elements.

(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) Any of a set of numbers which extends the set of real numbers by including infinitesimals and infinities, and is used in nonstandard analysis.

(mathematics) The minimum, taken over all planar representations of a link or graph, of the number of times it crosses itself.

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

To queue; to wait to be served by being assigned a number and waiting for that number to be called after all previous numbers have been served in order of assignment.