Find the dissimilar term: P49, T4, Z64, K9.

Let's analyze the relationship between the letter and the number in each term:
* P49: The positional value of P is $16$. Sum of digits = $1+6=7$. Squaring it: $7^2=49$.
* T4: The positional value of T is $20$. Sum of digits = $2+0=2$. Squaring it: $2^2=4$.
* Z64: The positional value of Z is $26$. Sum of digits = $2+6=8$. Squaring it: $8^2=64$.
* K9: The positional value of K is $11$. Sum of digits = $1+1=2$. Squaring it: $2^2=4$. However, the term given is K9.

Therefore, K9 is the dissimilar term.