trianglenumbers
nounUK /ˈtraɪæŋɡəl ˈnʌmbəz/
US /ˈtraɪæŋɡəl ˈnʌmbərz/
Triangle numbers are numbers you get by adding counting numbers one by one, like 1, 3, 6, 10.
The first four triangle numbers are 1, 3, 6, and 10.
OTHER MEANINGS
2. Numbers that can be arranged as dots in a triangle shape.
Ten is a triangle number because you can make a triangle with four rows of dots.
3. A sequence in math where each number is the sum of all counting numbers up to that point.
The fifth triangle number is 15, because 1+2+3+4+5 equals 15.
4. A pattern of numbers used in puzzles and games.
She solved the puzzle by spotting the triangle numbers in the list.