On the Subject of Flipping Triangles

No, you’re not upside down.

Please see Appendix 1PP1NG for identifying modules in the Triangles family.

This module will have 9 triangles on it. Each of them is either grey or off. To solve the module, press the valid triangle each time. Pressing a triangle will turn it off and change the next valid triangle. If no more valid triangles are present on the module after pressing a triangle, the module will solve. Note that triangles turn off when pressed, regardless of validity.

Identifying the valid triangle

Start with 0. For each triangle in the order shown on the image in the top-right part of this page, double your number, and add 1 if it is grey, or 0 if it’s off. Finally repeatedly sum the number’s digits together to get a new number until it becomes a single digit. The valid triangle is the one in this position in reading order (with the topmost triangle being 1).