nice suggestion but i'm looking for a more generalized assignment like recursion, pointers, etc to gauge the logic/skill of the applicant. What small app specs should i give him?

I want him to create an app that have those criteria like recursion, linked list or pointers.
I'm thinking of letting him create an app and generate 5000 random text and put it in a database. Then on each prime numbers put a "this is a prime number" text. Something like that.

Do you have another example in mind?