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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- …
2012rcampion's user avatar
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 …
2012rcampion's user avatar
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. …
2012rcampion's user avatar
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 …
2012rcampion's user avatar
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.
2012rcampion's user avatar
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 …
2012rcampion's user avatar
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: $$\left(138 + \sqrt{320}\right)^{570} \approx 10^{1249.9041}$$ …
2012rcampion's user avatar
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 …
2012rcampion's user avatar
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:
2012rcampion's user avatar