Yes, the number 21 is indeed a triangular number. Other triangular numbers are 6,10, and 15.
21
The 20th triangular number is 20*21/2 = 210
32 is not a triangular number. The first few triangular numbers are 1, 3, 6, 10, 15, 21, 28, 36, 45, ...
No, 23 is not a triangular number. Here are a few examples of triangular numbers: 21, 28, 55, 45, 78 and 91.
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.
Yes, the number 21 is indeed a triangular number. Other triangular numbers are 6,10, and 15.
21
The 20th triangular number is 20*21/2 = 210
21
32 is not a triangular number. The first few triangular numbers are 1, 3, 6, 10, 15, 21, 28, 36, 45, ...
28"21" but to be extra smart the answer is "The seventh triangular number is twenty one."
No, 23 is not a triangular number. Here are a few examples of triangular numbers: 21, 28, 55, 45, 78 and 91.
No. The first few triangular numbers are 1, 3, 6, 10, 15, 21, 28, ...
36 is the only square number that is also a triangular number between 20 and 40.
47 is not a triangular number. Triangular numbers less than 100 are 1, 3, 6, 10, 15, 21, 28, 36, 45, 55, 66, 78, and 91.
6, 10, 15, 21, 55, 91...