Most efficient way to store a big DNA sequence?

Question

I want to pack a giant DNA sequence with an iOS app (about 3,000,000,000 base pairs). Each base pair can have a value A, C, T or G

Answer 1

If you don't mind having a complex solution, take a look at this paper or this paper or even this one which is more detailed.

But I think you need to specify better what you're dealing with. Some specifics applications can lead do diferent storage. For example, the last paper I cited deals with lossy compression of DNA...