The first six triangular numbers are : 1,3,6,10,15,21.
However, sometimes the first triangular number is regarded as 0 (zero) so you then have 0,1,3,6,10,15 as the first six triangular numbers.
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Triangle numbers or triangular numbers are those numbers that can form an equilateral triangle when counting the objects. The first five triangular numbers are: 1, 3, 6, 10, 15.
If I remember correctly, the triangle numbers are 1, 3, 6, 10, 15... It is like racking up billiard balls or bowling pins. If the first number is 1, then the 3rd number is 6.
Triangluar numbers or triangle numbers are numbers formed from the summation of all the numbers smaller than them. The first few triangle numbers are 1,3,6,10,15,21... If you think of a pyramid with a base of two blocks, and one on top, there are three blocks. If you add a base of three to that pyramid, you have six blocks. Then ten, and fifteen and so on. That is why they are called Triangle numbers.
1.4.9.16.25.36
Triangular numbers are numbers that are formed from the sum 1+2+3+4... The equation for the nth triangle number is (n2+n)/2 In this case, we want the sixth triangle number, so feed this into the equation: (62+6)/2 =(36+6)/2 =42/2 =21 Thus the sixth triangle number is 21.