The triangular numbers are
1, 3, 6, 10, 15, ...
and are calculated as:
t1 = 1
t2 = 1 + 2
t3 = 1 + 2 + 3
tn = 1 + 2 + ... + n
The formula for the sum tn = 1 + 2 + ... + n is:
tn = n(n+1)/2
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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.
6 and 10 are triangular numbers that make 16.
the answer is of course 12
There are an many triangular numbers that are also square numbers. Simply put, the sum of two consecutive triangular number equals a square number. Examples include 1 and 36.
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.