Inside code (i*i) in loop

#1

why are we doing ii ?
/////////////////////////////
for(int i=2;ii<=n;i++) in for loop ?

#2

because if we analyse any number
eg
36 -> factors are 2 , 3 , 4, 6 , 13,12,9,6
all prime factor occur before the square root of the number which can be written either as
i <= sqrt(n) or
i * i <= n
so for optimisiation purpose we do
i* i <= n

#3

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