Is 100001 a prime number

Answer 1

100001 is a big number and it is not easy to tell if the number is a Prime number or not.

But we can always start with numbers like 2, 3, 5, 7, 11, 13 etc, which are also prime numbers.

Dividing 100001 each time with prime numbers can be tedious.

So we have to check by using divisibility rules.

Check with the first few prime numbers...

Let's check with 2:

100001 is an odd number so it is not divisible by 2.

Let us check if the number is divisible by 3:

Sum of digits = 1+0+0+0+0+1 = 2

[If the sum of digits is not a multiple of 3, then the number is not divisible by 3.]

Sum of digits is 2 and 2 is not a multiple of 3(or 2 is not divisible by 3).

So, 100001 is not divisible by 3.

Let's check with 11 after checking with 5 and 7:

Sum of digits at odd places = 1+0+0 = 1

Sum of digits at even places = 0+0+1 = 1

Difference = 1-1 = 0

[If the difference is zero or a multiple of 11 then the number is divisible by 11.]

So 100001 is divisible by 11.

Since 100001 is divisible by 11, it means 100001 has more than two factors.

So, 100001 is not a prime number.