There are a couple of ISO standards whose numbers I have memorised.
These include 639 (language names), 646 (ASCII), 3166 (country codes), 8601 (dates and times), 8859 (8-bit character encodings), and 10646 ("Unicode", kinda-sorta).
(I feel as if I "should" know the ISO standard specifying the "A" series of paper sizes such as A4, but I don't.)
Oh! And there's also ISO 2022. But I had to hunt a while in my memory and only vaguely remembered there were several 2's involves, and tried out 2212, 2122, 2022, to see what would fit, but had to confirm my memory on Wikipedia. So that doesn't really count. And there's also one that gets referenced moderately often that includes terminal emulation codes, I think, but I can't think of it right now.
What about you?