There are 13 left-handed and 21 right-handed spirals on the cacti in the photograph. what is special about these numbers?
a. the value of the 21st term of the fibonacci sequence is 13.
b. they are consecutive terms in the pyramidal sequence.
c. they are consecutive terms in the fibonacci sequence.
d. the value of the 21st term of the pyramidal sequence is 13.

C.They are consecutive terms in the Fibonacci sequence.

Step-by-step explanation:

The Fibonacci Sequence is the series of numbers: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, ...

Each number is the sum of the two numbers that come before it.

The square pyramidal numbers are: 1, 5, 14, 30, 55, 91, 140, 204, 285, 385, 506, 650, 819, ...

Therefore, we can see given numbers of cactus , 13 and 21 respectively are the consecutive terms of Fibonacci sequence.

Thus, Option C is the right answer.