# Octagonal Numbers

The Octagonal Numbers are those of the form $3n^2 – 2n$. Taking the digital roots of the octagonal numbers gives the repeating sequence 1, 8, 3, 4, 2, 6, 7, 5, 9,…

Octagonal Numbers by Suman Vaze

Jigsaw is a talented chess player and fervent climber.

• ### Things to make

Platonic shapes from tube maps, flexagons, and more mathematical craft

• ### Optimal Pac-Man

Ghostbusting with graph theory
• ### Reinventing 2D

What a difference a matrix makes