Find the odd one from the given series: $4,16,36,64,100,121,196,256$

Let's look at the squares forming the series:
* $4=2^2$ (Even number square)
* $16=4^2$ (Even number square)
* $36=6^2$ (Even number square)
* $64=8^2$ (Even number square)
* $100=10^2$ (Even number square)
* $121=11^2$ (Odd number square)
* $196=14^2$ (Even number square)
* $256=16^2$ (Even number square)
All numbers in the series are squares of consecutive even numbers except $121$, which is the square of an odd number ($11$). Thus, $121$ is the odd one out.