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nachiketajoshi t1_jaexluq wrote on February 28, 2023 at 11:06 PM

There are something like 335 area codes in USA (first 3 digits).

After that, you have 9000000 possible combinations for a 7-digit number. N=1st×2nd×3rd×4th×5th×6th×7th=9×10×10×10×10×10×10=9×106N=9000000

9000000 x 335 = 3,015,000,000, which is roughly 9x the population of USA. And, we have not yet exhausted all the possible the area code (first 3 digits).