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119 votes

Make 0 0 0 0 = 8

A lateral thinking answer:
let_the_coding_begin's user avatar
114 votes
Accepted

Make 0 0 0 0 = 8

I think that This is because This works and is valid because
El-Guest's user avatar
  • 32.3k
75 votes

Make 0 0 0 0 = 8

because
Teemu Piippo's user avatar
64 votes

Make 0 0 0 0 = 8

Lateral thinking!
TheSimpliFire's user avatar
52 votes
Accepted

Make 5 5 5 5 = 19

Here's one way I found: Or, using just the characters explicitly allowed in the question:
Riley's user avatar
  • 14.5k
43 votes

Maximize the number of factorials in your solution to 6 5 4 3 = 1

The answer is
Bennett Bernardoni's user avatar
43 votes

x⌊x⌊x⌊x⌋⌋⌋ = 2020

Observations to give lower and upper bounds: So we know for sure Now the whole thing becomes Contradiction ... and now I realise my implicit assumption that Going back to those two observations at ...
Rand al'Thor's user avatar
42 votes
Accepted

First digit of 3^2020

I think it's a Explanation: According to my calculator (this answer was posted before the no-computers tag was added), If we're not allowed to use computers, I would The same trick is used to ...
Glorfindel's user avatar
  • 28.1k
39 votes

Make 0 0 0 0 = 8

let me try:
malioboro's user avatar
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37 votes

Make 5 5 5 5 = 19

If the double factorial is allowed, then I propose WolframAlpha agrees that the result is 19.
Anastasiya-Romanova 秀's user avatar
37 votes
Accepted

Make 6 5 4 3 = 81

I thought a bit too much but I finally got it:
Tipping Octopus's user avatar
37 votes

First digit of 3^2020

This is one way to do it with the help of binary numbers. It is called exponentiation by squaring. EDIT Thanks to the few comments that pointed out the mistakes in my calculations. I was very lucky to ...
Alain Remillard's user avatar
34 votes
Accepted

x⌊x⌊x⌊x⌋⌋⌋ = 2020

Answer: Explanation:
trolley813's user avatar
  • 11.3k
33 votes

Make 0 0 0 0 = 8

It's different:
JMP's user avatar
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31 votes
Accepted

Professor Halfbrain and the sum of the digits of all divisors

Professor Halfbrain's theorem is Proof
hexomino's user avatar
  • 137k
31 votes

Make 5 5 5 5 = 19

I am quite sure it is not the expected answer but it is the immediate answer comes into my mind.
Keith's user avatar
  • 321
30 votes

Make 0 0 0 0 = 8

Evaluation:
u-ndefined's user avatar
  • 5,181
30 votes
Accepted

What makes this polynomial a square number?

Of course, $x=0$ is an answer, so let's look for non-zero ones from now on. If the given expression is a perfect square, so is Now we try to estimate it by "nearby" perfect squares. One ...
Ankoganit's user avatar
  • 19.6k
29 votes

Make 6 5 4 3 = 81

My solution: Just normal Math
user51872's user avatar
  • 301
29 votes
Accepted

Shifting a digit from right to left

I think the answer is Proof Computer check
hexomino's user avatar
  • 137k
29 votes

Number of divisors equals square root

The number of positive divisors is a multiplicative function in the number theoretical sense. The square root is also multiplicative. We can therefore proceed prime factor by prime factor. If ...
loopy walt's user avatar
  • 21.3k
27 votes

Make 5 5 5 5 = 19

For the 5s For the 1s (previous edit)
Bennett Bernardoni's user avatar
25 votes
Accepted

Integers around a circle with consecutive pairs adding to a square

Step 1: Step 2:
A. P.'s user avatar
  • 5,948
25 votes
Accepted

What number follows up next? Part 2

OEIS doesn't list this sequence. After analyzing the pattern, I come to the conclusion that (one) answer is Explanation: EDIT (05/06/18): I submitted this sequence to OEIS and it has (finally) been ...
NAMELESS's user avatar
  • 1,370
25 votes

Nice no-computers way to find limerick primes?

Obviously a is one of {1,3,7,9} and a,b are coprime. Also, b can't be a multiple of 3 regardless (else our number is a multiple of 3). That leaves 23 possibilities (4 for a, 6 for b, but we can't have ...
Gareth McCaughan's user avatar
25 votes

How to find the 2021st integer co-prime to 15

The trick is this:
Deusovi's user avatar
  • 147k
24 votes
Accepted

Professor Halfbrain and numbers with many zeros

The Professor is: Because:
Paul Evans's user avatar
  • 9,431
24 votes
Accepted

Fun with numbers: solve A to E

Explanation: Recap to see that all of them fit:
Marius's user avatar
  • 18.2k
24 votes
Accepted

Consecutive integers around a circle

I have a solution using 448 consecutive integers. The integers are centered on a number which I will call $c$, which is: ...
isaacg's user avatar
  • 7,148
23 votes
Accepted

Mother and Daughter

We are looking for The only way I know of to find one is I think So
Gareth McCaughan's user avatar

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