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Number patterns

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Triangle numbers

Triangle numbers can be represented as a triangle of dots.

The triangle numbers are:

Triangle numbers represented by dots aligned to make equilateral triangles
Question

What is the next triangle number after 21?

Answer

The next row of the triangle will have 7 dots. So the next number is

1 + 2 + 3 + 4 + 5 + 6 + 7 = 28

28 dot equilateral triangle

Activity

Number patterns activity

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