The ornamental design for a tabletcomputer, as shown and described.
1.-4. Tablet computer
1.1 : Front
1.2 : Back
1.3 : Left
1.4 : Right
1.5 : Top
1.6 : Bottom
1.7 : Perspective
1.8 : Perspective view of state of use
3.1 : Front
3.2 : Back
3.3 : Left
3.4 : Right
3.5 : Top
3.6 : Bottom
3.7 : Perspective
3.8 : Perspective view of state of use
4.1 : Front
4.2 : Back
4.3 : Left
4.4 : Right
4.5 : Top
4.6 : Bottom
4.7 : Perspective
4.8 : Perspective view of state of use
The broken lines showing the keyboard are for the purpose of illustrating environment and form no part of the claimed design; the broken lines showing portions of the tablet computer form no part of the claimed design.