In number theory, an Erdős–Nicolas number is a number that is not perfect, but that equals one of the partial sums of its divisors. That is, a number n is an Erdős–Nicolas number when there exists another number m such that
∑ d ∣ n , d ≤ m d = n . {\displaystyle \sum _{d\mid n,\ d\leq m}d=n.}
The first ten Erdős–Nicolas numbers are
24, 2016, 8190, 42336, 45864, 392448, 714240, 1571328, 61900800 and 91963648. ((sequence A194472 in the OEIS)) They are named after Paul Erdős and Jean-Louis Nicolas, who wrote about them in 1975.
See also Descartes number, another type of almost-perfect numbers
References