# COOL MATH: Very Triangular Numbers

This essay starts with a puzzle I posed on twitter, which led to a next puzzle, and a next. My thanks to  @republicofmath and @sted304A for computing very very triangular numbers, and to @daveinstpaul for an elegant idea giving a proof.    OPENING PUZZLER:   The sequence of numbers that are the sum of two […]

# COOL MATH: Sand Piles

OPENING PUZZLER  Stack $$n$$ coins at the origin on the number line and let them spread across it according to the following rule: Identify a stack with two or more coins on it and then “fire” that stack.  That is, move two coins off the identified stack and set one coin one unit to the […]