C# beginner

OK, first semester in C# and just starting to work on it.  Haven't programmed in a long time, kinda stumped on this one.  The assignment is to determine if a number is prime, and if its not, to factor it.  I know what a prime number is in my head, but I don't really know how to put that into code.

Thanks.

>>1
pseudocode:
IS-PRIME(N)
    if N ends in a 3, 5 or 7
        yeah
    else
        nah
sorry it's kind of hand wavy, I'm a researcher lulz