Yutaka Nishiyama (西山 豊, Nishiyama Yutaka, born 21 October 1948) is a Japanese mathematician and professor at the Osaka University of Economics, where he teaches mathematics and information. He is known as the "boomerang professor". He has written nine books about the mathematics in daily life. The most recent one, The mystery of five in nature, investigates, amongst other things, why many flowers have five petals.