Gaudi used mathematics extensively in his buildings. He made great use of minimal surfaces (such as the helicoid) which appear often in nature (for example, soap bubbles). He also used quadrics such as the hyperboloid and paraboloid. He was quoted as saying:
Paraboloids, hyperboloids and helicoids, constantly varying the incidence of the light ... make ornamentation and even modelling unnecessary
I also love his mosaics which use a technique called Trencadis. Here are some images of his work... there is a maths lesson or ten in here somewhere!