First of all, thank you all.
1 is called Identity number of multiplication (I think).
21 is not a prime, but 11 should be a prime per definition "A number that
has itself and unity as its only factors." Isn't it?

"Mike H" wrote:

hi,

Every odd number isn't prime, the correct definition is that a prime number
has 2 (and only 2) distinct natural number divisors.

Mike

"muddan madhu" wrote:

may be this ?

=IF(MOD(A1,2),"prime","not prime")



On Oct 9, 8:56 am, danpt wrote:
Does Excel has a formula to check if an integer is a prime number or not?
Thank you