Which of the following sequences is different from the rest?
a. $1,4,9,16$
b. $1,8,27,64$
c. $2,6,12,23$
d. $1,16,81,256$

Let's look at the mathematical logic behind each sequence for the first four natural numbers ($n=1,2,3,4$):
* Sequence a: $1,4,9,16\to$ This represents the squares of consecutive natural numbers: $1^2,2^2,3^2,4^2$.
* Sequence b: $1,8,27,64\to$ This represents the cubes of consecutive natural numbers: $1^3,2^3,3^3,4^3$.
* Sequence d: $1,16,81,256\to$ This represents the fourth powers of consecutive natural numbers: $1^4,2^4,3^4,4^4$.

All sequences a, b, and d follow a consistent power-based pattern ($n^k$).

* Sequence c: $2,6,12,23\to$ This sequence does not follow a uniform standard power relation. (A standard sequence of products of consecutive numbers would be $1\times 2=2,2\times 3=6,3\times 4=12,4\times 5=20$, but here the last term is $23$).

Therefore, sequence c is different from the rest. Sequence c corresponds to option (B).