Questions tagged [no-computers]
A puzzle designed to be solved without using calculators, online decoders, or computer programming. Using a computer to type and post the answer is allowed; the spirit of this tag is to make people solve the puzzle on their own.
918 questions
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When is the next "Factorion" date?
A "Factorion" date is a date such that when written to either one of M!+M!+D!+D!+Y!+Y!+Y!+Y! (MM/DD/YYYY), D!+D!+M!+M!+Y!+Y!+Y!+Y! (DD/MM/YYYY) , or Y!+Y!+Y!+Y!+M!+M!+D!+D! (YYYY/MM/DD) is ...
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Find a number whose divisors' factorials add up to a given number
This question did never came out in any contest.
If $\sum_{d\mid n} d!=$ ...
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Is 1,111,111,111,111 prime? Not even close!
Inspired by this question, I pose one that leans in the opposite direction.
The number 1,111,111,111,111 is not only composite. It has a factor quite small compared with what one might expect for a ...
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With the help of the cows, can you determine the secret code?
To allow new users to solve this puzzle and earn reputation points, I encourage all users whose reputation is 200 or more to not post an answer until 48 hours after this question is posted. Thank you!
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Show that the area of the region inside this square and regular pentagon is greater than 3/4
A square and a regular pentagon, each of area 1, are coplanar and concentric. Show that the area of the region inside both shapes is greater than 3/4.
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Cracking a coded quintic equation
They say you cannot solve most quintic equations (ones containing the fifth power of a variable) without specially designed functions. But if you can find the sequence, you can identify the positive ...
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Is 1,111,111,111,111,111,111 prime?
Now I am rereading the good old book "The Canterbury puzzles and other curious problems" by Henry Ernest Dudeney. In the introduction he presents the following illustration of puzzle ...
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How many trails from A to C?
Consider the following graph (3 edges between A,B; 3 edges between B,C; 2 edges between A,C).
How many trails are there that start from vertex A and end at vertex C? Two trails are considered the same ...
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Place a nonzero digit into some of the white cells of the grid
Place a nonzero digit into some of the white cells of the grid. Shaded cells must remain blank. No digit can repeat in a row or column. In each row, the sum of the digits must be equal to some fixed ...
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Reverse-Engineering an Incomplete Information Logic Puzzle
This is my first post to puzzling stack exchange, please let me know of any feedback you have. It's an original puzzle I made myself.
The Puzzle:
Alice and Bob are in prison for life for convincing ...
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What is the minimum number of games played between Arun and Disha?
Arun and Disha played several games of table tennis. At five different points during the day, Arun calculated the percentage of the games played so far that he had won. The results of these ...
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When the number of coprime integers is the product of the split numbers
The number 1434 has the special property that there are exactly 14×34 positive integers between 1 to 1434 (inclusive) that are relatively prime to 1434.
Of course, one can simply write a simple ...
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Tiling a rectangle with heptominoes [duplicate]
An n-omino is a two-dimensional polygon composed of n congruent squares glued together via the edges. For instance, the 4-ominoes are the Tetris shapes.
It is famously known that one can tile a 6-by-...
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Find the Hidden Rule!
Handmade Puzzle.
Solve the puzzle, and find the hidden rule. (This is not evil.)
[Notations / Rules]
0. Latin Square - Each rows and columns should have distinct digits from 1~9.
1a. - Maximum cell: ...
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Determine if there exists a future date such that the sum of digits of MM/DD/YYYY is equal to ⌊√yyyy⌋
Note: I created this puzzle.
Determine if there exists a future date such that the sum of digits of MM/DD/YYYY is equal to $\lfloor\sqrt{yyyy}\rfloor$, where MM is the month, DD is the day, and YYYY ...
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