A Belphegor number (also known as a Beelphegor number or a beastly palindromic prime) is a palindromic number of the form . Numbers of this form are named after the
demon Belphegor (or Beelphegor), one of the seven princes of Hell and the demon of
inventiveness. The th
Belphegor number is given by
giving the first few numbers for , 1, ... as 16661, 1066601, 100666001, 10006660001, 1000066600001,
... (OEIS A232449).