Over the last few days, I’ve had to hop between hotels. The process has left me confused about my constantly-changing room number. But I’m not the only one struggling to keep track.

After a session here at the APS, I met a similarly bewildered scientist. He was flitting between some of the many parallel sessions in the convention centre, and couldn’t remember which room he was meant to be in next. Then he cried, “ah, but of course, it was room 314. I won’t forget that, it’s Pi.”

Pi, of course, is the ratio of a circles’ circumference to its diameter (and it begins 3.14159 26535 8979). Such are the advantages of being into mathematics… Unfortunately, I haven’t been able to think of any fundamental constants that start 409.