What is the Fibonacci sequence?

The Fibonacci sequence begins 0, 1, 1, 2, 3, 5, 8, 13, 21, and continues by adding the two previous numbers to get the next. It was popularized in Europe by Leonardo of Pisa (Fibonacci) in 1202, though it was known earlier in Indian mathematics. The sequence shows up remarkably often in nature: the spiral of a sunflower’s seeds, the arrangement of leaves, pinecones, and the branching of trees frequently follow Fibonacci numbers. As the sequence grows, the ratio between consecutive terms approaches the golden ratio, about 1.618, a proportion long associated with aesthetics in art and architecture.