GL Paper 8 multiple choice

[Azure]

Hello
Question 16 in this paper is
there are 10 cans in this stack
the stack is 4 cans high

1
2 3
4 5 6
7 8 9 10

(Sorry these numbers supposed to show a diagram of the cans )

How many cans would there be in a stack like this that was 8 cans high?

I remember there si a formula for this question kind but I cannot remember it. Can anyone prod my memory?

[arcana]

1
2 3
4 5 6
7 8 9 10
11 12 13 14 15
16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31 32 33 34 35 36

= (n*(n+1))/2 = (8*(8+1))/2 = (8*9)/2 = 72/2 = 36

[Azure]

Thank you so much As soon as I read it I thought of course!

[berks_mum]

If my memory is serving me right, will this be a sequence of triangular numbers?

Addition of 8 consecutive numbers -

1+2+3+4+5+6+7+8