ModStep is 50% off ($9.99) for a one day special sale (and then they have a special announcement too!)
ModStep is a very powerful MIDI Sequencer for the iPad. The things this app can do are pretty sweet, especially in terms of modulation! It is a bit of a bugger to figure out though so be warned but if you want to sequence other apps, hardware or even out to computers then this is an app to look at!
The second app is on a 30% sale and this is probably the app you should be using for notes!
Notability ($6.99) is just a rock solid, versatile, and packed full of features app that I use constantly to take notes with. I use it in front of the class as my whiteboard. I use it in meetings. I have all of our music theory notes for every single class in it. The list goes on and on.