There are 13 left handed and 21 right handed spirals on the cacti in the photograph. what is special about these numbers

Ahh, the most beautiful sequence there is. This is known as the Fibonacci Sequence and it occurs in real life in an actual cactus (or succulent I believe).

Whats so special about it is that the sequence goes like this

0, 1, 1, 2, 3, 5, 8, 13, 21, 34

The next number is the sum of the digits. It can be represented as x (n-1) + x (n-2)