Type $k^2$.

Context Panel: Sequence≻$k$≻$1\,5$ 
Click OK.
See Figure A-3.2(a)

Context Panel: Select Element≻3

Alternatively, convert the sequence to a list, name the list, and use selection-brackets:
Context Panel: Conversions≻To List
Context Panel: Assign to a Name≻$q$ 

To unassign the name $q$ interactively, use the Variables palette. (See Table A-1.2.)

Use the seq command to create the sequence (see Section 10.2), and assign to the name $q$.

Selection-brackets extract the third item in the sequence.

$q≔\mathrm{seq}\left(k^2\,k\=1..5\right)\:$

$q\left[3\right]$

Unassign the name $q$ with the unassign command.