Ladder Problems https://www.mathematische-basteleien.de/ladder.htm
There are two similar triangles (yellow) and you have (##) x:b=b:y.
Dein Suchergebnis zum Thema: have
Mandelbrot Set https://www.mathematische-basteleien.de/mandel_set.htm
Provided that you have a palette with 10 colours (0 to 9).
Danzig-Wonneberg/Ujescisko https://www.mathematische-basteleien.de/wonneberg2.htm
Lidl and Netto have opened their supermarkets.
Square Numbers https://www.mathematische-basteleien.de/squarenumber.htm
You can rather say that natural numbers and square numbers have the same amount,
Cube Numbers https://www.mathematische-basteleien.de/cubenumber.htm
>The numbers 2, 9, 16, 28, 35, 54, 65, 72, 91 have sums with 2 cubes at least: 2,