The Jewish calendar has a 19 year cycle, where Years 3, 6, 8, 11, 14,
17, and 19 (גוחאדז”ט) are leap years (מ), they have a second Adar. The other
years are *Pashut*, simple years with only one Adar.

Obviously we can calculate the position of the current year in the cycle by doing mod 19.

```
5773 % 19 == 16 ; // This year is pashut, but next year is a leap year.
```

How can we write a single equation that we can use to test if a year is a leap year or not.

There is a solution on Wikipedia, but I’m more interested in the process than the final answer.