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# identifier | What is behind the DNI letter An ID number is the most common way to identify us. Although some may have doubts about what a Meaning of different numbers The fact that the General Directorate of Police provides these numbers randomly to each police station. However, the letter of the document is not the same. The fact is that this is determined according to a mathematical algorithm with intent Detect possible errors Like fake products.

### The true meaning

This algorithm is based on the well-known clock arithmetic, which is used to describe cyclic processes, such as the passage of time in hours, days, or months. based on periodic relationship For example, after twelve o’clock you go back to one o’clock, after the last day of the month you go back to day one and at the end of December you start January. This calculation is based on reaching a number and once you reach it, it starts all over again.

As far as DNI is concerned, the modulo match 23. The process consists of calculating the remainder of dividing the DNI number by 23. Based on this remainder, a letter is assigned according to the table of number and letter equations.

### what does that mean?

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If a number is changed between the first five by adding or subtracting 3, for example, the difference with the original number is 3 followed by at least three zeros, which is is always a multiple of 24.

Unit 23 is not chosen by chance, but because it is a prime number, It will avoid giving any kind of errors. By changing one digit, the difference between the two numbers is the ones followed by the zeros, which will never be a multiple of 23.