(number theory) Any of a sequence of numbers having the property that the sum of the divisors of each, excluding itself, is equal to the next number in the sequence; in the case of the last number of the sequence, the sum of the divisors, excluding that number, is equal to the first number of the sequence.

A dimensionless number used in heat transfer calculations, giving a simple index of the ratio of the heat transfer resistances inside of and at the surface of a body.

Synonym of mass number

Alternative spelling of number-crunching

(mathematics, obsolete) A fraction.

Alternative form of tailnumber

(mathematics) A number consisting of a whole number and a fraction, such as 11½.

(geometry, topology, mathematical analysis) The total number of times a given curve travels counterclockwise around a specified point.

(chronology) A number showing the year of the lunar or Metonic cycle. It is reckoned from 1 to 19, and is so called from having formerly been written in the calendar in gold.

The smallest number bigger than any finite number named by an expression in the language of set theory with a googol symbols or less.