Can you identify the five-digit sphenic palindrome
- where the sum of its digits is a palindromic prime,
- where of one its factors is a multi-digit palindromic prime, and
- the sum of its factors is also a palindromic prime?
Can you identify any other sphenic palindrome that has these characteristics?
A sphenic number is a positive integer and product of three distinct primes.
A palindromic number is a number that is the same when written forwards or backwards.
Suppose the required palindromic number is xyzyx. The sum of its 5 digits <= 45, i.e., is a 2 digit number. The only 2 digit palindromic prime is 11 which must be the sum of the digits.
Since xyzyx is a prime, x cannot be 0, even or 5, i.e., x is 1 or 3.
Therefore, feasible solutions are 12521, 13331, 14141, 31313, or 32123.
A little factoring finds the only one that meets all the criteria is 32123 with digital sum 11, factors 7x13x353 of which 353 is a palindromic prime, and sum of factors 373 which is another palindromic prime.
Nice problem!