Let me think. I would like to spit gold. I would like to be able to produce people and destroy them after they have finished the work I made them do for me. I would like to be able to make all the life freeze for a set amount of time...
I could go on, but I am afraid someone will eventually put me away. So those are just examples.
Oh, and I would like to be able to turn people into toads. I have a few candidates already.
Wait, 'superhuman' you said. Well, I am not interested in becoming more human than what has been imposed on me already. It's boring as hell.
If you want to read about math prodigies, I highly recommend you to read about people like Leonhard Euler, Carl F. Gauss, John Von Neumann or people who have contributed to mathematics and are recognized as brilliant mathematicians. At least they have things named after them. Not just random people who have set records in things that are completely useless.
Also, I suggest you to read the story of Andriy Slyusarchuk, the Ukrainian "Doctor Pi" who claims that he has memorized millions of the digits of pi. He's now in prison for several crimes including faking a medical degree, illegal surgeries as a brain surgeon without a medical degree, frauds, etc.
As a mathematician, I feel obliged to say that Shakuntala Davi was not a mathematician at all. She was a magician. Definitely not a math genius, not even close.
You might be interested in the lives of autistic savants, Sarah. Research "autistic savants" and watch Rain Man if you haven't watched it already.
My favorite superhuman ability is having a photographic (eidetic) memory.