Ask A Scientist Mathematics Archive

name         Silvana
status       student
age          11

Question -   Can negative numbers be Prime or Composite?
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It makes no difference. Prime-ness has to do with multiplication /
division. A number is prime if and only if it is divisible only by itself
and the number '1'. Whether the sign is positive or negative does not
matter. Since you ask about "primality" and so may be interested in number
theory. You might be interested in a very "simple" conjecture (a
mathematical statement that is surely "true" but which has never been
proved. It is called Goldbach's conjecture. Every even number (that is one
that is divisible by "2") is the sum of at least one pair of prime numbers.
Examples: 2=1+1, 4=3+1, 6=5+1, 8=5+3 or 7+1,
12= 11+1 = 7+5 .... There may be more combinations of primes but there is
always at least one. And just subtracting the number "1" does not always
work. For example 10=9+1 is not an example because the number "9" is not
prime, but 10=7+3 is a prime pair.
    But no mathematical proof for this apparently "simple" theorem in number
theory has been found. Funny thing these simple counting numbers.

Vince Calder
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