13, 21 - it is the Fibonacci sequence
The next two numbers in the sequence are... 45 & 54.
An arithmetic sequence is a line-up of numbers in which the DIFFERENCE between any two next-door neighbors is always the same.
This list of numbers is the list of prime numbers. Following 11, the next two numbers in the list are 13 and 17.
Fibonacci found a way to present mathematical numbers so that each number in the sequence is the sum of the two previous numbers. For example, if the sequence starts at 0 and 1, then next number in the sequence is 1, the next number would be 2, and then the next number would be 3, and then 5.
2and1
9
12 12
13, 21 - it is the Fibonacci sequence
The next two numbers in the sequence are... 45 & 54.
-63 and -81
Two consecutive numbers are added together to get the next one. 1,1,2,3,5,8,13...
11 and 8
An arithmetic sequence is a line-up of numbers in which the DIFFERENCE between any two next-door neighbors is always the same.
That'd be the Fibonnaci sequence (this time without the wikipedia URL :P)
If the first two numbers are 0, 1 or -1 (not both zero) then you get an alternating Fibonacci sequence.
This list of numbers is the list of prime numbers. Following 11, the next two numbers in the list are 13 and 17.