It is prime.
991 is a prime, the others are composite.
The positive integer factors of 991 are: 1, 991
1 and 991
991 and 1.991 is a prime number and only has factors of 1 and 991.
0.0091
991 is a prime and so has no proper factors.
991 is already prime. No tree is required.
sqrt(991) = 31.480 (to 5 sf)
76.2308
No. 991 is not evenly divisible by four.
Yes, 991 is a prime number. It has no factors other than 1 and itself.