Hello Puzzling Stack Exchange! While part 1 of the PSE School of Enigmatics remains unsolved, I've got part 1 of another puzzle series for you to solve. I'm in no way affiliated with Numberphile; however, I am highly appreciative of the channel, and find their content to be invaluable. Enjoy!

URGH. You've run out of brown paper; and, quite frankly, there's only one way to get more - crack open the Numberphile vault.

Sneaking your way past two security kangaroos, you make your way to the vault.

The Vault

You notice that the buttons 2, 4, 6 and 8 are located on hinges. You carefully pry open these buttons, and find yourself with a sudoku-esque conundrum:

The Vault, with buttons pried open

Hmm. How hard could this be? You punch in 314159265, the first 9 digits of Pi, and immediately you are startled by the sound of grinding as the nearest missile launcher points at you. One more failed attempt, and you're toast.

You try prying open the other buttons, but to no avail. However, you do notice that the 5 button is written funnily, and pops out of the display. You can't pry it open, though.

What could the password be?

Hint 1

Can the sudoku actually be solved?

Hint 2

Yes, the sudoku can be solved. But then again, even a sudoku puzzle consisting of an empty board can be solved.

Hint 3

Perhaps if there isn't one solution to the sudoku, could the puzzle have to do with more than one of its possible solutions?

  • 2
    $\begingroup$ My only immediate observation so far is that the 5 looks suspiciously like an upside-down question mark with the dot smudged. $\endgroup$ Jul 14, 2017 at 9:57
  • 1
    $\begingroup$ "You've run out of brown paper; and, quite frankly, there's only one way to get more - crack open the Numberphile vault." - I don't think this is true. I know one more way but I don't want to describe it here. $\endgroup$
    – Marius
    Jul 14, 2017 at 13:03

5 Answers 5


It has been four days since you encountered this door, and it has stumped you. You are hungry, have to use the restroom, and regret not simply turning around and buying more brown paper at Brown Paper Mart™

No. You can beat this. You hear the voice of the hint fairy whispering in your ear "don't solve the sudoku, just look at the branches of possibility to solve it". Maybe that's delirium from the hunger? You don't care, you trust it either way.

The 5 button stands out, literally and figuratively. It must mean something. Perhaps if we were to draw a grid from the other grids...it becomes a complete grid, with 5... or whatever this odd symbol is, in the middle.

Then we just use our old sudoku logic to fill out what we can.

sudoku picture

That's what we can get with no assumptions outside of thinking we know the middle number in each square. So the password?

193451789 The buttons themselves tell us the order to input it.

Well, it's either that or

The keypad is a ruse and the door was unlocked. I mean, there is no enter key, after all.

  • $\begingroup$ I guess your answer is correct. I assume the button in the middle with the funny 5 is some kind of 'enter' key, because it has a highlight on the top and left edge and a shadow on the bottom and right edge. Furthermore claims the description 'the 5 button...pops out of the display'. $\endgroup$
    – Tobi Obeck
    Jul 18, 2017 at 20:24
  • $\begingroup$ You push the door open. Well done! $\endgroup$
    – Zerium
    Jul 19, 2017 at 5:24


"What could the password be?" Taken literally: it could be anything except 314159625, which we know is wrong.

My reasons:

  1. I don't think I can figure it out :p

  2. The sudoku hint suggests that you can solve an empty sudoku any way you like, and because the sudoku in this is "purposefully" missing information, I get the implication that there is intentionally not enough information to deduce a single code.

  3. "Lateral thinking" tag, though I'm new and I don't know if I'm allowed to use that as a hint to the intended solution. Misread the tag, but "logical deduction" suggests similar.

  • $\begingroup$ "You glance back at the vault, thinking of all the unused brown paper stacked up in there. You can almost smell the mustiness of its recycled texture! You would never walk away from such a challenge like this, especially where the rewards are so lucrative." Nope, I definitely had a straightforward answer in mind when making this riddle :) $\endgroup$
    – Zerium
    Jul 14, 2017 at 13:08
  • $\begingroup$ Alright, back to the drawing board. It was worth a shot, but glad to know there's a serious answer. $\endgroup$
    – Raeservoir
    Jul 14, 2017 at 13:12

Wild, partial, but possible answer

Since OP uses the term 'solve' quite broadly, and the sudoku itself gives too few hints, it is possible that

The sudoku is irrelevant, and what matters is the numbers upfront.

Therefore, the password is


Of course, after that, you need to

Run, before the missile hits you.


After the missile (probably) destroy the vault, go inside and collect your brown papers.

  • $\begingroup$ ... and if the paper wasn't brown already, it is now? $\endgroup$
    – Rubio
    Jul 14, 2017 at 12:22
  • 1
    $\begingroup$ Hahaha - actually it's not that funny, because you realised a little too late that the missile is auto-tracking! Goodbye William :) $\endgroup$
    – Zerium
    Jul 14, 2017 at 12:26

I partly solved the sudoku. I assumed that the 5 in the middle can be used as a small number to solve the sudoku.

I am not sure which 9 digits should be the ones to solve the puzzle, neither is it clear in which order various possible numbers should be aligned.
My best guess is:

749856231 or 749856213.

enter image description here

  • $\begingroup$ I am not sure which 9 digits should be the ones to solve the puzzle. Perhaps the puzzle is not meant to be "solved"? $\endgroup$
    – Zerium
    Jul 16, 2017 at 23:46

I would say : 759836214

You need to solve the sudoku, and the code is the number under the 5 (?) panel.

  • $\begingroup$ Unfortunately that is not the correct answer. You cannot actually solve the sudoku - there is (purposefully) too little information given. $\endgroup$
    – Zerium
    Jul 14, 2017 at 10:59
  • $\begingroup$ How did you solve the sudoku? I can get 9, 2 and 6, but I don't see how to get the other ones without any assumptions. $\endgroup$ Jul 14, 2017 at 11:02
  • $\begingroup$ @ZizyArcher Perhaps you will find the two hints in the question to be of help :) $\endgroup$
    – Zerium
    Jul 14, 2017 at 11:03

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