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A mathematical puzzle whose solution is heavily based on the arithmetic properties of the integers. Use with [mathematics]
4
votes
Can powers sum to rational squares?
Consider the sequence:
$$
a_n=x^n+y^n
$$
We can write this as a recurrence relation:
$$
\begin{align}
a_n&=(x+y)\ a_{n-1}-xy\ a_{n-2} \\
a_n&=(x+y)\left(x^{n-1}+y^{n-1}\right)-xy\left(x^{n-2}+y^{n- …
20
votes
Accepted
Professor Halfbrain and the powers of 2016
This answer is an improvement on Milo Brandt's answer, and is based on "Formes linéaires en deux logarithmes et déterminants d′interpolation" (M. Laurent, M. Mignotte, and Y. Nesterenko) (which I got …
15
votes
Accepted
A table filled with greatest common divisors
Essentially what we need to do is find a lower bound on the sum:
$$
\sum_{i=1}^{n}\sum_{j=1}^{n}\operatorname{gcd}(i,j) \tag{1}
$$
This is the total of the entries in the $n\times n$ table of GCD's. …
4
votes
What is the number..?
The Chinese remainder theorem renders this type of problem easy. However, in this case the answer is even easier:
The Chinese remainder theorem tells us that there are an infinite number of number …
17
votes
Accepted
Comparing exponents - no computers!
The right side increases with $n$, and we know that
Therefore, for $n\geq 3$,
Now we only have to check $n=2$ and $n=1$ by hand.
3
votes
Weighing in 2015 different ways
(Please tell me why this works, I have no idea!)
Hint 2b suggests that there is a relationship between binary representations of coin weights and continued fractions. I assumed that this relationshi …
11
votes
The year 2016 is approaching
By brute-force search, yes. I started by searching over all tuples $(r,s,t)$ less than $1000$, stopping at the first example I found:
$$\left(138 + \sqrt{320}\right)^{570} \approx 10^{1249.9041}$$ …
8
votes
Accepted
Introducing S-sequences: which is the shortest to contain all integers 1 to 20?
Answer to part c):
Found with the following Python code:
from heapq import heappush, heappop
best_n = 0
candidates = [(1, [1], set((1,)))]
while candidates:
prev_max, prev_list, prev_set = heap …
9
votes
Accepted
Break into Goldbach's safe
Adding
Translating the exponents from decimal to ASCII gives:
The title "Goldbach's safe" and name "C. Goldbach" likely refers to: