Is it possible to use an Android tablet as a MIDI sequencer with a Yamaha Clavinova CLP-170 digital piano? My Yamaha piano has a USB port.
I can't speak from experience since I don't own any Android devices, but in theory, yes it is possible.
Assuming your Android tablet can handle class-compliant MIDI devices (i.e. if it can act as a USB host), and presuming that your piano acts as such a device when plugged in via USB (I can't say for sure with either of your devices, but this is not uncommon), then all you need is some sequencer app that can write to a generic MIDI interface. A quick Google search suggests that several sequencer apps exist, although I don't know if any support communicating to a USB device.
If your piano isn't class compliant, it should still have MIDI DIN in and out ports, so a generic USB MIDI interface with DIN cables such as this one ought to communicate with it in a similar way.
If CLP-170 is class compliant then it is possible starting with Android 3.1 if the device supports USB Host mode. I can tell you most of the phones do not support USB Host mode but tablets usually do. I own a Nexus 4 and a Nexus 7.
I developed an app which is a lot more complex then a midi sequencer, my app acts like an Arranger (Auto accompaniment software, midiArranger) and it works great with Nexus 7, Nexus 10 and other. It is free and currently in beta testing. I asked the community what other devices they use and I will get back to you. I plan to develop a MIDI sequencer too, the ones I saw out there are not too good.
If your device has a micro usb port you will need an USB OTG Cable like this.
You can definitely connect your Clavinova to an android device. Since your digital piano has USB type B port, all you need is a USB A to B cable, and then depending on which port your Android has, you'll need a USB type A (female) to C (male) if your android device has a USB type C port OR USB type A (female) to microUSB adapter if your device has a microUSB port. Once you've connected you can do tons of music-related things starting from learning how to play the piano and ending with recording your own songs. You can read all about it in this article.