Carnival of Mathematics 225

Welcome to the Two-Hundred and Twenty-Fifth Carnival of Mathematics. Let’s start with facts about 225: Octagonal numbers are always fun: And then we can always think in gradians for a hexadecagon where the outside angles shown are 225 gradians (202.5 degrees or 1.125π radians). (Thanks David JONES f

Carnival of Mathematics 225

Welcome to the Two-Hundred and Twenty-Fifth Carnival of Mathematics.

Let’s start with facts about 225:

gif of 15x15 grid animating white squares highlighting in the sequence of divisors of 225.
  • 225 = 152
  • 225 = (1 + 2 + 3 + 4 + 5)2 
  • 225 = 13 + 23 + 33 + 43 + 53
  • 225 is a highly composite odd number
  • 225 is the smallest number that is a polygonal number in five different ways.
  • 225 is a refactorable number.

Octagonal numbers are always fun:

225 shown as an octagonal number with nested octagons meeting at the same vertex

And then we can always think in gradians for a hexadecagon where the outside angles shown are 225 gradians (202.5 degrees or 1.125π radians). (Thanks David JONES for the suggestion).

a hexadecagon (16 sides) with angles interior and exterior highlighted in blue and orange with the angle marking on the exterior convex angles.

Submissions, news, and blogs:


Numberphile has a new video:


Mastodon Posts:

Submitted Twitter posts: