What number follows 13 and 21 in the Fibonacci series?

In mathematics, the Fibonacci numbers are the numbers in the following integer sequence, called the Fibonacci sequence, and characterized by the fact that every number after the first two is the sum of the two preceding ones:

1 , 1 , 2 , 3 , 5 , 8 , 13 , 21 , 34 , 55 , 89 , 144 , …

Often, especially in modern usage, the sequence is extended by one more initial term:

0 , 1 , 1 , 2 , 3 , 5 , 8 , 13 , 21 , 34 , 55 , 89 , 144 , …

By definition, the first two numbers in the Fibonacci sequence are either 1 and 1, or 0 and 1, depending on the chosen starting point of the sequence, and each subsequent number is the sum of the previous two.

The Fibonacci sequence is named after Italian mathematician Leonardo of Pisa, known as Fibonacci. His 1202 book Liber Abaci introduced the sequence to Western European mathematics, although the sequence had been described earlier as Virahanka numbers in Indian mathematics.

More Info: en.wikipedia.org

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16 Comments

Betty Jo Bailey

I learn a lot from your test. 👍

Corey Taylor

It's as easy as 1 ,1, 2, 3!

Corey Taylor

233, 377, 610, 987, 1597, 2584, 4181, 6765...

dmarkc

Never seen any practical use for it.

Jas Newman

Steve Tingle, Shall we assume "geology" was a typo for "geometry"? Sunflower seeds also follow the pattern. Regarding the article, if 0+1 were considered the starting point, the pattern would never progress beyond 1. Best to stick with 1+1 as the starting point.

Mic Fenst

Joris van Pelt, Kind of. You need initially to define the first two terms.

Steve Tingle

I was introduced to it as the Golden Progression in geology in college, with various examples found in nature, like the number of spirals in a pine cone the number in one direction and the number in the opposite direction are always two consecutive numbers from the progression, and as the picture shows the proportions of a Nautilus shell fo0llow it.

Jaimi McEntire

Alan Oswald, one use is for estimating times & costs depending on how "large" the job is. Because of unknowns, the larger the job, the more things can interfere.