A palindromic number is a number that is the same, backwards and forwards, e.g. 12321. It so happens that for almost all numbers, repeatedly adding a number to its reverse eventually produces a palindromic number. For example:

78 + 87 = 165
165 + 561 = 726
726 + 627 = 1353
1353 + 3531 = 4884 …

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