TI-BASIC (nspire), 15 bytes
f(n):=isPrime(n #TI-BASIC (nspire), 15 bytes f(n):=isPrime(n UsesUses the CAS isPrime() builtin. The environment by default adds an extra parenthesis on the end of the input, making it f(n):=isPrime(n) when the function is defined in the interpreter.