(mathematics) Any of four topological invariants associated with a topological space. The smallest Listing number counts the number of connected components of a space, and is thus equivalent to the zeroth Betti number.

plural of Listing number

plural of Fresnel number

(optics) A dimensionless quantity (denoted F), such that for an electromagnetic wave passing through an aperture and hitting a screen, F=(a²)/(L𝜆) where a is the characteristic size (e.g. radius) of the aperture, L is the distance of the screen from the aperture, and 𝜆 is the incident wavelength.

(mathematics) A positive integer which is divisible by the sum of all of its digits.

plural of Harshad number

plural of square number

(mathematics) Any integer which is the product of some integer with the integer itself.

(mathematics) A positive integer that is divisible by every one of its digits.

(number theory) The subbranch of number theory which applies techniques from geometry to the study of algebraic numbers.