The series presented is a variation of the Fibonacci sequence, which typically starts with 0 and 1, or, as seen here, with 1 and 1. In a standard Fibonacci sequence, each number is the sum of the two preceding ones.
Here’s how it breaks down:
- 1 (1st)
- 1 (2nd)
- 2 (1 + 1 = 2, 3rd)
- 3 (1 + 2 = 3, 4th)
- 5 (2 + 3 = 5, 5th)
- 8 (3 + 5 = 8, 6th)
- 13 (5 + 8 = 13, 7th)
- 21 (8 + 13 = 21, 8th)
However, if we closely analyze the series, the number that stands out as not fitting the pattern is 4.
While all the other numbers belong to the Fibonacci sequence, 4 does not follow the rule and instead is an isolated value that interrupts the flow of the series. Therefore, 4 is the number that does not belong in this particular sequence.