: Mathématiques: untouchable number

mathematical analysis > calculus > sequence > integer sequence > untouchable number

number > natural numbers > untouchable number

untouchable number

In mathematics, an untouchable number is a positive integer that cannot be expressed as the sum of all the proper divisors of any positive integer. That is, these numbers are not in the image of the aliquot sum function. Their study goes back at least to Abu Mansur al-Baghdadi (circa 1000 AD), who observed that both 2 and 5 are untouchable.
(Wikipedia, The Free Encyclopedia, https://en.wikipedia.org/wiki/Untouchable_number)

http://data.loterre.fr/ark:/67375/PSR-GJNBQKR4-C

RDF/XML TURTLE JSON-LD Date de création 26/07/2023, dernière modification le 18/10/2024

Loterre