What are the first four triangular numbers, starting with 1 ? \( \square \) (Use a comma to separate answers as needed.)

The first four triangular numbers, starting with 1, are 1, 3, 6, and 10. These numbers represent the total number of dots that can form an equilateral triangle. For example, with 3 dots, you can create the first triangular formation, while 10 dots can be arranged to form a larger triangle. Triangular numbers are not just fun in math; they pop up in various real-life situations! Think about arranging items in triangle shapes, like those cute little holiday trees made of ornaments. They're also significant in combinatorics, often used to calculate combinations or to summarize data in a triangular array. So, next time you see a triangle, think about the numbers hidden inside!