This isn't exactly a how-to guide, but here are some ways that I've found that keep me thinking while inputting numbers for my internship.
-Have a Netflix account or find a show on Hulu that you like a lot, but don't mind listening to. Likewise, find a good podcast. Preferably something entertaining-- my current go-tos are Supernatural, X-Files, Better Off Ted, Community, and gaming podcasts. I like watching police procedurals as well, but make sure that the episodes have enough twist to be surprising, but not enough that if you miss a clue while inputting numbers that you're not confused when they unveil the true criminal at the forty-five minute mark. Try some history or science podcasts, especially when it comes to subjects you don't know much about. You may not get everything the first time around, especially if you're multi-tasking, but you can always listen to it again. Audiobooks are good too.
-Make a good playlist with exciting music. Hell, try out some new music! You'll be at your computer for a while, so it might as well be something you haven't listened to before.
-Take breaks. Stretching your wrists, getting up once in a while, and finding a comfortable place to work are really important. If you're going to be at your desk for a really long time, do some desk yoga. There are YouTube videos for that which will walk you through it. Relaxing your eyes is also incredibly important. Focus on a far corner or object, and just focus your eyes on and off. Computer monitors can really mess up your eyesight, and there are programs out there that change the overall color of your monitor along with the hour, to match the more natural light of the sun.
-Your room is a trap. So find somewhere else to work. In school, your dorm room functions as your office/bedroom/living room/whatever. If you tend to work at your desk really well, then work at your desk. I have a friend who prefers to work on her bed, and she is dynamite at it. Me, I need somewhere else that isn't my desk, since I've essentially shaped my thinking process to desk equals art/fun internet time. For things other than small homework assignments, I tend to go elsewhere. It also means that you're not staring at the terrible white walls that invariably come with dorm rooms, and you get to pretend that you're hanging out with other people.
-Stay hydrated. If you get a cup of coffee, tea, soda, whatever, make sure you also get a glass of water along with it. When you finish a cup of coffee, switch to a glass of water. For one thing, it will keep you from feeling like electricity is running through your veins. After a couple of cups, coffee can be really dehydrating for your body, and switching to water for a bit will be good for you. Eating food is good too-- I know I forget to eat if I get really absorbed in my work, so getting something like a muffin or scone that you can eat with your fingers is nice.
I hope that some of these tips help out in some way! These are just some thing that I've learned over the last couple of years, as well as things that I've figured out during the course of my internship.