Only Mariah, Whitney, MJB, and R. Kelly rank higher. Description:
With a staggering 15 No. 1 singles on R&B/Hip-Hop Songs, Janet Jackson owns the most toppers on the tally in the past 25 years. Only R. Kelly and Usher, with 11 each, come close to the diva in that span of time. (Even Jackson's superstar older brother Michael trails, with just eight in that span of time.) Between the years of 1985 and 2001, Janet Jackson was an unstoppable force on the charts, landing more top 10s than any other act: 27. Going further, from 1985 through 2004, Jackson amassed 33 consecutive top 40 hits, beginning with the No. 40-peaking "Fast Girls" through the No. 18 hit "I Want You."
http://www.billboard.com/column/the-juice/the-top-50-r-b-hip-hop-artists-of-the-past-1004127916.story#/column/the-juice/the-top-50-r-b-hip-hop-artists-of-the-past-1004127916.story?page=5