The sequence $T_{2,m}$ in Guy's 1967 paper A problem of Zarankiewicz describes the maximum size of a collection of $4$-subsets of $\{1,\dots,m\}$ such that every $3$-subset is in at most two of the $4$-subsets. It had not been added to the OEIS until the time of my work on Zarankiewicz's problem,...
Intro
Two numbers are a reversed multiple pair if they satisfy the following property:
$$
a\times b = reversed( (a-1)\times b )
$$
Here, \$reversed()\$ means to reverse the digits of a number (e. g 123 becomes 321.)
Example
$$
a=6, b=9,
6\times9=54,5\times9=45
$$
As you can see, \$45\$ is the rev...
In Q3 2021 I finalized my research around three vote close/reopen and I was pretty happy with the outcomes - as were the sites that got to test it out. While the benefit to each site was different, the most important thing was that there were no negative impacts of that test and all of the sites ...
Originally we had implemented keyboard shortcuts as a user script. We have now finally made the change to have them integrated into the site.
When you go to the Edit Profile & Settings page on your profile, and then select the Preferences submenu, you’ll find a new checkbox labeled Enable keyboa...
Given a ragged list of positive integers, where the maximum depth is \$d_\text{max}\$, return the same list, except for every element \$e\$, its depth is \$d_\text{max}+1-d_e\$ (where \$d_e\$ is the depth of that element).
Your output should contain the minimal number of brackets, and you can ass...
The prime numbers
We have 226 questions about prime numbers at the time of writing. Almost every single one of these involves some adaptation of the “canonical prime checking code” or the “canonical prime generator”. Primes are notorious for not really conforming to any mathematical symmetry in ...
