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| I used Mathematica to create the following puzzle. [A playable version is here][1]. Normal sudoku rules apply. Digits cannot repeat along diagonals except when they appear on an arrow. In which case, they must repeat but only in the cell indicated... |
| At stackexchange I [posted a question][1]: > In the paper [Space Vectors Forming Rational Angles][2] a special set > of tetrahedra is mentioned. > > "The remaining three are in the R-orbit of the tetrahedron with > dihedral angles (?/7, 3?/7,... |
| Notice that $2021$ is a concatenation of consecutive integers: $20\sim 21$ Also $2021$ is a product of consecutive primes: $43\times 47$. What is the next number with both of these properties? $24502451$ is close, $4943\times 4957$ but... |
| Awhile ago we added GraphData[{"UnitDistance", {21, 2}}] to Mathematica. Graph[GraphData[{"UnitDistance", {21, 2}}], VertexLabels -> "Name"] ![heptagon bracing][1] I found the graph while researching unit-distance graphs... |
| Jim Williams recently finished a multi-year search for all simple perfect squared squares up to order 37. More details will eventually be at [squaring.net][1]. For orders 21 to 37, there are {1, 8, 12, 26, 160, 441, 1152, 3001, 7901, 20566, 54541,... |
| FiniteGroupData is missing a few group generations, so I've filled in some holes. One of the groups is Frobenius 21. ... |
| I was amused by the post [1-D Cellular Automata With a Twist][1], so I thought I'd take a look. ![enter image description here][2] Here's rule 420. Clear[a]; tab=Table[{a[0,k]=0, a[k,0]=0},{k,0,800}]; a[0,0]=1; ... |
| What is the smallest set so that differences of members of the set give all values from $1$ to $n$? This is a famous problem worked on by [Paul Erd?s](https://en.wikipedia.org/wiki/Paul_Erd%C5%91s), [Marcel J. E.... |
| 7 years ago William Somsky showed me how to divide an equilateral triangle into 13 strictly acute isosceles triangles. When I noticed the image, I realized I could now solve it exactly. Seems to need roots of order 10 polynomials. ![Somsky... |
| Code for a nice Venn 5. ![venn5][1] pp=RootReduce[2CirclePoints[5]/(EuclideanDistance@@CirclePoints[5][[{1,2}]])]; sp=Join[Table[2.12CirclePoints[10][[Mod[n-2,10,1]]]+pp[[2]],{n,1,9}], ... |