Discovery and Validation of a High-Density sub-Neptune from the K2 Mission, Néstor Espinoza, Rafael Brahm, Andrés Jordán, James S. Jenkins, Felipe Rojas, Paula Jofré, Thomas Mädler, Markus Rabus, Julio Chanamé, Blake Pantoja, Maritza G. Soto, Katie M. Morzinski, Jared R. Males, Kimberly Ward-Duong, Laird M. Close, Submitted on 28 January 2016, last revised 14 July 2016