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Fibonacci Day

Fun · Nature · November 23

Fibonacci Day looks at the number sequence where each term is the sum of the two before it, and where those numbers turn up in nature.

Fibonacci Day falls on Monday, November 23, 2026. That is 27 days away.

Start with 1 and 1. Add them to get 2, then keep adding the last two numbers: 3, 5, 8, 13, 21. That running list is the Fibonacci sequence, and this page is about it.

The rule is simple enough to teach a child, yet the numbers show up in places nobody arranged them. Count the spirals on a pinecone or in the seed head of a sunflower and you will often land on two neighboring Fibonacci numbers, one count going clockwise and one going the other way. Many flowers have petal counts from the sequence too, with three, five and eight being common.

There is also a ratio tucked inside. Divide any Fibonacci number by the one before it and, as the numbers grow, the answer settles closer and closer to about 1.618, the value known as the golden ratio. Draw squares with sides of 1, 1, 2, 3 and 5, fit them together, and a curve through their corners makes a tidy spiral.

Marking the day can be as quiet as a walk with your eyes on the ground. Pinecones, pineapples, artichokes and cauliflower all reward a careful count, and a pencil helps. Some people write the sequence out as far as their patience allows, which is usually further than they expected and less far than the numbers go.

The sequence is named for Leonardo of Pisa, an Italian mathematician who was known as Fibonacci and wrote about it in a book on arithmetic.

Ways to celebrate

• Count the spirals on a pinecone in both directions.
• Write out the sequence until the numbers get unwieldy.
• Draw a Fibonacci spiral using squares on graph paper.
• Count the petals on a few flowers in your neighborhood.
• Divide neighboring Fibonacci numbers and watch the ratio settle.

Dates

All national days on November 23

Also on November 23

• National Espresso Day
• National Cashew Day
• Eat a Cranberry Day

Categories: Fun daysNature days