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.
ISO 8601 contains way too many obscure formats. RFC 3339 is pretty much a subset and defines only sensible ones. It also allows 2018-02-05 08:02:43-00:00 (no T and explicitly specifying no timezone)
in this cartoon, the lady character says : "Easy - - just memorize it as the first three prime numbers, if you realise you couldn't remember what came after 2 and started to panic and get them increasingly wrong"
first 3 primes : "2, 3, 5"
forgot 2nd : "2, ..., 5"
then, get the next primes : "7, 11"
... increasingly wrong : "not 518 ? ?"
No, either it's a bad one or I'm missing something.
https://explainxkcd.com/wiki/index.php/2937:_Room_Code
Cueball and Megan are on vacation or otherwise traveling, and receive a code for their hotel room. Megan gives a seemingly nonsensical and unhelpful mnemonic by which Cueball can remember it... which, inexplicably, actually helps Cueball to remember the code. Cueball becomes VERY angry on realizing this.
The first three prime numbers are actually 2, 3, and 5. So this technique easily identifies the first two digits "02". "05" is slightly wrong because it's not the second prime number, it's the third. And "18" is more wrong because it's not actually a prime number, it's 2 x 3 x 3.
So the mnemonic itself doesn't really provide the method for remembering the code. Instead, figuring out how to apply the bogus mnemonic will reinforce your memory of the code.
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.
The second half is 3 digits. I'd just hard code memorize it.
0x0518
The first half is something between 0. It's a easy pattern.
020518
The last missing digit must be something simple and deductible from other numbers if I put it to the last. As all other numbers (0, 518) are even, it should be 2.