[seqfan] Palindrome Product Mystery

[Hans Havermann]

All palindromes can trivially be written as the product of two palindromes: p = 1 * p, so let's let's decide that neither the multiplier nor the multiplicand may be 1. That gets rid of the prime palindromes. Most of the composite palindromes can still be written as the product of two palindromes (>1), so let's focus on the ones that can't: 212, 606, 747, 787, 8008, ... When I plot these I get more-or-less straight, seemingly parallel line segments that make discrete jumps to another line segment. Looking at the data, we have (for example) no solutions between 88188 and 891198, 1694961 and 2699962, 3522253 and 6527256, and so on. Why?