The ornamental design for a tabletcomputer, as shown and described.
FIG. 1 is a front perspective view of a tablet computer showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left-side view thereof;
FIG. 5 is a right-side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof;
FIG. 8 is a front perspective view, in which the tablet computer is provided in a connected position to illustrate an example environment; and,
FIG. 9 is a left-side perspective view, in which the stand portion of the tablet computer is provided in an open position and the tablet computer is provided in a partially open position to illustrate an example environment.
The broken lines shown in the drawings represent portions of the tablet computer which form no part of the claimed design.