TOPICS
A natural number 
such that
 |
whenever 
(
and 
are relatively prime)
and 
. (Here, 
means that 
divides 
.) There are an infinite number of such numbers, the first
few being 9, 15, 21, 33, 39, 51, ... (OEIS A033553).
The 
-numbers are the same as the 3-Knödel
numbers.
-Numbers." Simon Stevin 36, 71, 1962/1963.Sloane,
N. J. A. Sequence A033553 in "The
On-Line Encyclopedia of Integer Sequences."Weisstein, Eric W. "D-Number." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/D-Number.html
