A number theory problem by Dat Huynh
Number Theory
Level
3
Find the largest palindrome number that is the product of two two-digit numbers.
The answer is 9009.
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1 solution
I didn't have a good mathematical formula for solving this, so I simply used the process of elimination. Starting with 9999, 9889, 9779, I worked my way back until I got to 9009. Since 99 is the largest 2-digit number, I started with 99 and worked back until the opposing factor exceeded two digits, then moved to the next lower palindromic number and started again. Eventually I reached 9009, which is the product of 91 and 99. If there's a formula out there for this, I would greatly appreciate it if someone would post it here.