[ *July 16, 2001* ]

723121327 a peculiar palindromic prime

Carlos Rivera (email) reports

While working on a new topic for his website Carlos Rivera discovered

that the smallest Langford Prime Number as defined in Puzzle 144

turned out to be **palindromic** !

__Let me first give the general definition of such a number :__

*For every digit d in a ***Langford Number** there always exists another digit d

- to the right or to the left - at a distance of exactly d+1 digits,

and with all interjacent digits differing from d.

The smallest Langford PRIME Number is this curious **palindrome**

Between the digits 7 lie 7 digits all different from 7

Between the digits 2 lie 2 digits all different from 2

Between the digits 3 lie 3 digits all different from 3

Between the digits 1 there is only 1 digit different from 1

What are the following 5 palprimes of this same class ?

Related OEIS sequences are

A088285

Palindromes in which the sum of the internal digits = the sum of the external digits.

A088286

Primes in A088285.

Palindromic primes in which the sum of the internal digits = the sum of the external digits.