You can use GeoGebra to check if a number is prime, or to find prime numbers. This can be especially useful with large numbers where it can be difficult to figure out if they are prime or not. 
     GeoGebra Instruction 1
Algebra     View     under         View     in         Menu.         IsPrime(<Number>)
by typing it in Algebra View and inserting your number in the <Number> field.         
If               GeoGebra         returns               true,               that               means               your               number               is               a               prime               number.               
If               GeoGebra         returns               false,               that               means               that               your               number               is               not             a               prime               number. 
PrimeFactors(<Number>)
to find the prime factors of your number.
     GeoGebra Instruction 2
Open Algebra View under  
View in  
Menu. 
If you have a number—no matter if it’s prime or not—and you want to find the closest prime number that is bigger than your number, use the command
NextPrime(<Number>).
If you have a number—no matter if it’s prime or not—and you want to find the closest prime number that is smaller than your number, use the command
PreviousPrime(<Number>).