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This answer presumes you require exactly a 400-digit number.

This answer treats a 40-digit number as example.

Primes often can be found adjacent to the prime factorials. ref OEIS sequence A002110 (below).

Looking at that list, the 17th entry is a 20-digit number, P=32589158477190044730 . I first tried 1 less, which was composite. I next tried 1 more. [I used the established PariGP pgm's ispseudoprime function to test primality]. If this lacks success, progress upward from the start primorial until you find a prime, call it Pr1, by adding odd prime factors.

There are other similar maneuvers that could be used ... If the 2 primes need to be distinct, work up from P above by adding prime factors and checking primality. So, check (P+3), then (P+5), etc until you hit a 2nd prime. This is a bit more sophisticated than just checking higher odds ending in 1,3,7 or 9. In this case, adding 71 to our starting primorial gives the prime 32589158477190044803 another slightly higher (adding 179) is:

32589158477190044911

the product of the 2 is a 40-digit number.

The process leading to a 400-digit results mimics the example just shown.

http://www.research.att.com/~njas/sequences/?q=A2110&language=english&go=Search. http://wims.unice.fr/wims/

Q: Find two prime numbers if multiplied would generate a 400-digit number?

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All numbers can be multiplied that way. A prime number is one that can only be divided by one and itself.

Every rational number does.

They are prime factors.

They are called factors or divisors.

Apart from 1, the rest are all composite. square numbers can be multiplied by at least 1, themselves and the number that they are multiplied to get that far (or more)!!

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Any number can be multiplied to get the answer 441. For example 5 can be multiplied by 88.2 If the question was which number can be multiplied by itself, the answers are: -21 and +21

All whole numbers, when multiplied by two (2) are even numbers (Of course, this includes zero, which is an even number).

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Every irrational number, when multiplied by 0.5 will produce an irrational number.

No,because it doesn't make sence for ending numbers multiplied together make an ending number

All numbers can be multiplied that way. A prime number is one that can only be divided by one and itself.

A square number is multiplied by two of the same numbers.