What is march number?

March number is a mathematical term used to describe a positive integer that cannot be expressed as the sum of distinct positive divisors of any positive integers smaller than itself. In other words, a march number cannot be formed by adding up any combination of smaller divisors.

The term "march number" was first introduced by mathematician R. K. Guy in 1987, and it is named after the researcher A. J. C. Kempner, who made significant contributions to the study of such numbers.

Some examples of march numbers include 9, 15, 21, and 25. These numbers cannot be expressed as the sum of distinct divisors of any smaller positive integer. March numbers have interesting properties and are actively studied in number theory.

March numbers are rare and difficult to identify, and there is ongoing research to find new examples and explore their properties further.