Beelphegor number

A Belphegor number (also known as a Beelphegor number or a beastly palindromic prime) is a palindromic number of the form 1(0...)666(0...)1. 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 nth Belphegor number is given by B_n = 10^(2n + 4) + 666·10^(n + 1) + 1, giving the first few numbers for n = 0, 1, ... as 16661, 1066601, 100666001, 10006660001, 1000066600001, ... (OEIS A232449). A prime Belphegor number is known as a Belphegor prime.

Belphegor prime | palindromic number