Article numbers from January 2016
From the January 2016 issue, MDPI journals will use article numbers in place of the traditional method of continuous pagination through the volume. This step helps us to maintain a rapid, efficient production process by being able to define pagination as soon as a paper is accepted. We have recently made a number of improvements to article layout and production procedures, of which article numbers is just one component. You can read more about the changes at http://blog.mdpi.com/2015/12/01/a-new-look-for-mdpi-papers/.
For papers that use article numbers the page number will start from 1 and the citation needs only list the article number, e.g., Holmes, L.; LaHurd, A.; Wasson, E.; McClarin, L.; Dabney, K. Racial and Ethnic Heterogeneity in the Association Between Total Cholesterol and Pediatric Obesity. Int. J. Environ. Res. Public Health 2016, 13, 19 (article number: 19. http://www.mdpi.com/1660-4601/13/1/19).