Question

What square number will we get if we add

13 and 14 triangular numbers

Answer 1

And so the first four triangular numbers are 1, 3, 6, 10. Each one is the sum of consecutive numbers.

	1.
1 + 2	=	3.
1 + 2 + 3	=	6.
1 + 2 + 3 + 4	=	10.

so triangular nmbers are 1,3,6,10,15,21,28,36,45,55,66,78,91,105,120

sum of 13th and 14th triangular numbers =105+91 = 196

this is a square number because square root of 196 is 14.

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