Q: Is 643,640 a Prime Number?
A: No, 643,640 is not a prime number.
A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 643640 can be evenly divided by 1 2 4 5 8 10 20 40 16,091 32,182 64,364 80,455 128,728 160,910 321,820 and 643,640, with no remainder.
Since 643,640 cannot be divided by just 1 and 643,640, it is not a prime number.