figuratenumber
nounUK /ˈfɪɡərət ˈnʌmbə/
US /ˈfɪɡjərət ˈnʌmbər/
A figurate number is a number you can make by arranging dots into a shape like a triangle or square.
Ten is a triangular figurate number because you can arrange ten dots into a triangle.
OTHER MEANINGS
2. A number that counts the dots needed to build a regular geometric figure.
Six is a figurate number since six dots form a triangle.
3. Any number in a sequence built from growing shapes, such as triangular or square numbers.
The figurate numbers 1, 3, 6, 10 come from growing triangles.
4. A number that can be shown as a pattern of evenly spaced points.
Nine is a figurate number because its dots make a square.