No. The premise is that after 2 you have forgotten what comes next so in a panic you start wildly guessing. In this hypothetical premise, your guesses are then 5 and 18.
Back in reality (outside the hypothetical) you have now actually committed the sequence 2, 5, 18 to memory because you remember in the context of a story.
The first 5 prime numbers are 2, correct, horse, battery, staple.
Yes, the premise is that memory is really weird, and a stupid counterfactual “hook” still works as a memory hook.
This suggests that somewhere in our Galactic neighborhood are two gigantic apron clad men performing Bella Notte.
“Tony, galaxies don’t-a talk!”
So which galaxy is the male and which is the female or do galaxies have the ghey? 
The Milky Way is the smallest of the two galaxies, which suggest it is Lady. So we are in a female and Cocker Spaniel galaxy.
Perhaps our Milky Way is the male (smaller) Praying Mantis?
I can’t replicate his math.
Spaghetti is about 155 kcal / 100 grams, or 1.55 kcal/g. If we assume roughly the density of water, that’s also 1.55 kcal/cm^3, or 0.00155 kcal/mm^3.
Cooked spaghetti has a diameter of about 2.35 mm, or a cross-sectional area of 4.33 mm^2.
Andromeda is 2.537 million light years away, which is 2.4x10^25 mm.
Multiplied together, we get 1.61x10^23. That’s 161 sextillion, not septillion. My numbers are a bitt different from Munroe’s but not by a factor of >1000x. I expect that he made a mistake in saying septillion, perhaps thinking sept*3=21 for the exponent.
Or perhaps he really did mean lowercase-calories, which are 1/1000 the size of big-C Calories, even though no one actually measures food that way. So technically he was right, but in a confusing way.
Or maybe I made my own mistake there… entirely possible.
I think you could do better than Cesium-176. For instance, there’s a dry cell battery that’s already been going for almost two centuries:
It’s been driving a mechanical device, but a blinking LED would be no problem. And I’m pretty sure we could do even better today. Thousands of years seems plausible with the right design.
The LED or the driving electronics might be the limiting factor, but electronic lifetime is strongly dependent on how hard you drive them, so a dim, infrequently blinking LED could last almost indefinitely.
I know which strip you’re referencing, and I have legitimately started to use that method to generate work passwords.
It’s been years since I saw the strip and yet I still remember the password. I wasn’t 100% certain of the order but it looks like I got that right anyway.
I also used the method for a couple of master passwords. Unfortunately, most sites still have stupid special character requirements and so it doesn’t work well. But I use a password manager for these anyway.
I wonder if anyone has checked those password leak databases to see if anyone has actually used “correct horse battery staple”.
This reminds me of a conversation where someone hid a key, or a similar small valuable, at the bottom of their dog food bin. The assumption being it was a terribly inconvenient location. But it was only inconvenient to the homeowner, a burglar would just dump the dogfood on the floor and pick up the valuable in 3 seconds.
The often-missed caveat with the “Correct Horse Battery Staple” method is that the words must be chosen completely randomly. I’ve heard too many people say that they use that method, but improve on it by making the words a sentence so it’s easier to remember. And there goes the security.
You also lose some entropy bits if you reorder the words to be more grammatical.
The method I came up with was to get a list of common words and filter it down to 7,776 entries that had at least 5 letters each. I rolled a die 5 times to pick one entry (I suppose I could have made that easier with a D10). And I did that for 5 words. That’s over 64 bits of true entropy coming from physical die rolls.
Even password managers/generators can have issues. There was this recent story:
The man generated a “secure” password with a manager called RoboForm. It turned out that the manager just used the current date/time as the seed to its randomizer. It’s way easier to brute force all possible times in a range as compared to all possible passwords (though still non-trivial in this case since the time range was uncertain as well as the app settings).
Granted, the guy was lucky in this case that the password was hackable…
Hell, I remember the password on the 3.5-in (!) diskette I used the first time I installed AOL back in 1996: dust dregs.
“correct horse battery staple” isn’t even my password, though! It’s not like I remember it because I typed it in a zillion times.
I did remember my old ICQ password, though. They recently announced that they’re (finally!) shutting down, and I wanted to see if I could access my contact list. I’m sorta shocked that the account didn’t get hacked or anything in the 25 years since I used it. It’s not a great password, but isn’t totally brain-dead.