Simple design for printing in vase mode. If your seam does not fully melt together - don't worry. Part on it's own is strong enough to hold pens and pencils without much trouble. And due to extra inside perimiter it should hold it's shape just fine.
EDIT: I added v2 for those that have problem with their seams not connecting. My idea was that seams should hold just fine on their own, but after printing a few of v1 I realised that it's not always the case. v2 has two extra "rings" at the top that go all the way around, making the whole holder more rigid and "closed". Both versions are 100mm tall and can be scaled along Z axis in your favorite slicer software.
Set your slicer to vase mode. I used Cura 3.6 to slice it.
0.4mm line width
no special bed adhesion
5 bottom layers (bottom is 1mm thick so if you print with resolution other than 0.2mm you have to adjust).