3511 or 3501 21st Street SE 3511 3511 or 3501 21st Street SE is a rental apartment building with 10 floorplans available. It is located in Mandan. It has apartment amenities including in-unit laundry, and dishwasher. It has building amenities including elevator, garage parking, and fitness center. Cats and dogs are allowed, making it a pet-friendly building.