202020reglen

202020reglen, also known as the 2020 rule, is a mathematical curiosity that has gained attention due to its unusual properties. The rule states that for any four-digit number, if you subtract the number formed by the first two digits from the number formed by the last two digits, and then multiply the result by 1111, you will always get the original four-digit number. For example, for the number 2020, subtracting 20 from 20 gives 0, and multiplying by 1111 gives 0, which is not the original number. However, for the number 2021, subtracting 20 from 21 gives 1, and multiplying by 1111 gives 1111, which is the original number.

The rule can be expressed mathematically as follows: for a four-digit number ABCD, where A, B, C, and D are the digits, the rule states that (10C + D) - (10A + B) * 1111 = ABCD. The rule works because of the properties of the number 1111, which is a repunit and has the property that any number multiplied by 1111 will result in a number that is a multiple of 1111.

The rule was first discovered by a mathematician named John Conway, who shared it on his blog in 2013. Since then, it has been the subject of much discussion and analysis, with mathematicians and enthusiasts alike exploring its properties and applications. The rule has also been the subject of various online challenges and puzzles, with participants trying to find other numbers or patterns that exhibit similar properties.

While the rule is a mathematical curiosity and has no practical applications, it has become a popular topic of discussion in the mathematical community and among enthusiasts. Its simplicity and the fact that it can be easily verified make it an interesting subject for exploration and analysis.