please, can you help me to understand following formula (my math is a bit rusty,....)

I have a following function: where n=2 and −5.0 ≤ x_{i}≤ 5.0

f (x) = ∑^{n }x^{2}_{i }

i=1

So, my question is: since n=2 does it mean that the function needs 2 numbers on input, or just one? I think that only one, is it correct? For example if I use for x number 1 I will get f(x) = 2? And for x=2 I will get f(x) = 8?

thanks,

m.