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xkcd #2937: Room Code
(imgs.xkcd.com)
Alt text:
Sorry to make you memorize this random string of digits. If it helps, it can also double as a mnemonic for remembering your young relatives' birthdays, if they happened to have been born on February 5th, 2018.
I might be able to memorize it but would not trust my brain to not black out when I actually need the code. So a backup on a piece of paper or in my phone is crucial.