n = 10**8 s = [0]*(n+1) k=0 for i in range(2,n+1): if s[i]==0: k+=1 _________ s[j]=1
for i in range(i*i,n+1,i):
for j in range(i*i,n,j):
for j in range(i*i,n+1,i):
for j in range(j*j,n+1,i):