Numbril

Numbril is a term used in recreational mathematics and in some speculative fiction to denote a class of numbers tied to a relationship between a number and its digit-sum or base representation. There is no single canonical definition; different authors provide different formulations. A common informal definition in base 10 calls a numbril a positive integer that is divisible by the sum of its decimal digits, a property often described as Harshad or Niven numbers, while other writers extend the idea to alternate bases or to additional constraints. Because the term is not standardized, any discussion of numbrils should specify the exact rule being used.

In puzzles, numbrils are used to illustrate modular arithmetic, digit-sum functions, and base-conversion behavior, and they highlight how properties can change with the numeral system. In fictional contexts, numbril may appear as a mathematical resource, currency, or symbol with narrative significance, used to convey abstract numeracy or systematic thinking. The term’s application tends to vary by author and medium, reflecting its status as a nonstandard concept rather than a formal mathematical category.

See also Harshad numbers, digit sum, recreational mathematics. References to numbril are largely confined to puzzle collections and speculative fiction; discussions typically emphasize context-dependent usage rather than universal definitions.