Is 21 a Fibonacci Number?

21 is a Fibonacci Number if it is in the Fibonacci Sequence.

The Fibonacci Sequence starts with 1, 1, followed by the sum of the last two numbers in the sequence.

When we look at the Fibonacci Sequence, we see that the two Fibonacci Numbers before 21 are 8 and 13.

Since the sum of the last two numbers in the Sequence equals 21, we know that 21 is a Fibonacci Number.

Based on the information above, you can also calculate and conclude that the Fibonacci Number following 21 in the Fibonacci Sequence is 34, because 21 + 13 = 34.

Fibonacci Numbers
Look up another number to see if it is a Fibonacci Number.

Is 22 a Fibonacci Number?
Now you know if 21 is a Fibonacci Number or not. Go here to see if the next number on our list is a Fibonacci Number.