Curtis McEnroe posted a “tongue-in-cheek” derivation of a formula for the number of days in a month, ignoring leap years.

His result, in JavaScript:

```
function f(x) { return 28 + (x + Math.floor(x/8)) % 2 + 2 % x + 2 * Math.floor(1/x); }
```

His derivation is quite logical. I made a shorter alternative using a different technique, which I will leave for the reader to puzzle out.

function f(x){return 28+(62648012>>x>>x&3); }