Php change a number into another number that can be changed back to the original

Question

Using PHP, I\'m trying to encode a number into another number that I can decode back to the original number. The encoded string needs to be only numbers and should not contain a

Answer 1

Why not using a mathematicat operation on the original number? like x becomes x * y + z. you would only have to make the reverse operation to get the original number. consider using large enough prime numbers for y and/or z