(genetics) The number of copies of a gene or plasmid within a cell's genome. / (library science) The identification number assigned to a specific copy of a work.

Several. / Several of.

(mathematics) By means of, or in terms of, number theory.

A phone number as a mnemonic whose letters translate into numbers.

(mathematics) A mathematician who specializes in number theory

plural of number theorist

(US) A pencil which produces a specific shade of dark gray. One can usually identify a number 2 pencil by looking for the number "2" conspicuously emblazoned on the pencil. Often required for test-taking and the completion of official forms.

Any of the identification numbers used in an informal system for classifying catfish before they have an scientific name.

(organic chemistry) The number of carbon atoms in each molecule of a compound.

(physics) The numerical extent to which a quantum state is filled (in a system of many, identical quantum particles)