An invaluable source for travel information within the Netherlands is the route planner. It will give you precise directions on how to get where you want to go.
If you are coming from Schiphol, the most convenient way to get to Utrecht is by train. Both the train from Schiphol to Eindhoven (from platforms 1 or 2) and the train from Schiphol to Nijmegen (platform 3) stop at Station Utrecht Centraal. You can buy the tickets from the yellow ticket machines in the main hall of the airport using a credit card or a maestro card. A one way ticket costs €
8.50 (January 2015)
.
The address of the mathematics department (Departement Wiskunde, in Dutch) is
Budapestlaan 6
Utrecht