A Belphegor number (also known as a Beelphegor number) is a palindromic number of the decimal form 
, with 
zeros on each side of 666 for a nonnegative integer 
. These numbers are named after
the demon Belphegor (or Beelphegor), one of the seven princes of Hell and the demon
of inventiveness (Pickover n.d.). The Belphegor number with parameter 
is given by
 |
giving the first few numbers for 
, 1, ... as 16661, 1066601, 100666001, 10006660001, 1000066600001,
... (OEIS A232449).
A prime Belphegor number is known as a Belphegor prime.
