15th April

On this day in 1831 Gauss introduces the term "complex" for a + bi. Most of the 17th and 18th century writers spoke of a + bi as an imaginary quantity. Gauss saw the desirability of having different names for ai and a + bi, so he gave to the latter the Latin expression numeros integros complexos.

On this day in 2013 Google released an Euler doodle.