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0

1 (0+1)

3 (0+1+2)

6 (0+1+2+3)

10 (0+1+2+3+4)

15 (0+1+2+3+4+5)

21 (0+1+2+3+4+5+6)

Notice these are the numbers you can arrange into equalateral triangles.

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Wiki User

16y ago

What else can I help you with?