57.

A mentor carried it first.
Some numbers you inherit.

It's the favorite, asked at any counter,
guessed in any game.

57.3° is one radian,
the angle where the arc equals its radius.
Geometry's own unit, hiding in plain sight.

57 looks prime.
It isn't. (3 × 19, even Grothendieck slipped.)
Perfectly human. We keep it for that, too.

And a few more we're keeping to ourselves.