What is the first 400 digit prime number
:confused:

the first 400 digit prime number is
a number with exactly 400 digits (or place holders that are powers of ten),
is not a multiple of any number less than itself all the way to 2,
i.e. 2 times x will never equal this number Y that has 400 digits,
neither will 3 multiplied by any number below Y, and so on,
is the smallest prime with 400 digits, so don't randomly check 400 digit numbers
but start with the smallest 400 digit number and eliminate those that are composite.

a number is either composite (composed of two or more numbers as factors) or prime.

there are locations on the internet where I have heard you can look up to see if a number is prime or not.