Combinatorics · Counting · Palindromes · Digit sums · Divisibility by 9 · Residue classes · Case analysis by parity
Let \(n > 1\) be a natural number. How many \(n\)-digit numbers are palindromes and divisible by \(9\)?
(A number is a palindrome when its decimal representation is symmetric, that is, it reads the same from left to right as from right to left.)
Sign in to check answers, open hints, read the full solution, and track your progress. Statements are always free.
Serbian National Competition (Drzavno takmicenje) 2010, high school grade I, category A, problem 3. Organized by the Mathematical Society of Serbia (DMS). Source