A palindrome number is a number that remains the same when its digits are reversed. In other words, it has reflectional symmetry across a vertical axis. The term "palindromic" is derived from "palindrome," which refers to a word (such as rotor or racecar) whose spelling is unchanged when its letters are reversed. Palindromic numbers are most often considered in the decimal system, but the concept of palindromicity can be applied to the natural numbers in any numeral system. The first few palindromic numbers are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 22, 33, 44, 55, 66, 77, 88, 99, 101, 111, 121, .... Palindromic numbers receive most attention in the realm of recreational mathematics, and a typical problem asks for numbers that possess a certain property and are palindromic. For example, the palindromic primes are 2, 3, 5, 7, 11, 101, 131, 151, .... Palindromic numbers can be tested to see if they are palindromic in various programming languages, such as C, Java, and Python.