September 1 in Math: 109 Is Prime and 1/9 Is the Simplest Repeating Decimal

Happy new school year! It turns out that the date itself hides two elegant mathematical facts — a prime number and the simplest repeating decimal in existence.

September 1 as New Year’s Day

Here’s an interesting historical footnote: for nearly 200 years, there was no need for the word “school” in front of “year” — September 1 simply was New Year’s Day in Russia, following the Byzantine tradition. It was only Peter I who moved the celebration to January 1, in 1700.

109 Is Prime — and 1/9 Is the Simplest Repeating Decimal

For those who love numbers, the date 01.09 gives us two gems. First, 109 is a prime number — not divisible by anything other than 1 and itself. Second, 1/9 = 0.111… is arguably the simplest repeating decimal there is: a single digit, repeating forever, with a period of just one.

It’s a quiet reminder that even an ordinary calendar date, when read through a mathematical lens, can hold something worth thinking about.