suppose N is given to us.We need to find the sum of the number of multiples of x where x starts from x=1 to x=N and the multiple(let it be m) varies from x<=m<=N

eg:N=6

x=1 y1=6

x=2 y2=3

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x=6 y6=1

sum=y1+y2+y3…+y6

what is the best method to do it as the number i.e N can be very large i.e it can be in the order of 10^9