I believe the sequence you are referring to would be 0, 1, 1, 2, 3, 5, 8, 13, 21. This is known as the Fibonacci number. It is arrived at by adding the first two numbers to the left of the third number to get the third number and so on throughout the sequence. 0+1=1, 1+1=2, 1+2=3 and so on.
https://en.wikipedia.org/wiki/Fibonacci_number