[ July 16, 2001 ]
While working on a new topic for his website Carlos Rivera discovered
723121327 a peculiar palindromic prime
Carlos Rivera (email) reports
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
Palindromes in which the sum of the internal digits = the sum of the external digits.
Primes in A088285.
Palindromic primes in which the sum of the internal digits = the sum of the external digits.