Determine the smallest base ten positive palindrome with exactly 4 distinct prime factors.

(In reply to re(2): No Subject by Steve Herman)

Actually the following are the smallest five 5-digit palindromes with exactly 4 distinct prime factors,

10101 =  3 * 7 * 13 * 37
15351 =  3 * 7 * 17 * 43
17871 =  3 * 7 * 23 * 37
22422 =  2 * 3 * 37 * 101
22722 =  2 * 3 * 7 * 541

all smaller than the

24242 =  2 * 17 * 23 *  31

mentioned as being the smallest such illustrating the lack of 11 as a factor.

The first three appear in the first list, with prime factors up to 71, and the other two only in the second list, that doesn't have gaps.

Posted by Charlie on 2012-09-23 22:07:06