'21' = 9: Lady Gaga is on the edge of Billboard 200 glory, as her "Born This Way" is set to storm the summit of next week's chart.

Until then, Adele continues her impressive run at No. 1. The soulful singer/songwriter's sophomore set "21" becomes one of just 12 albums by a woman to lead the Billboard 200 for at least nine weeks.

Here is a look at all 12 titles - three of which belong to Whitney Houston - dating to the chart's launch as a weekly list March 24, 1956:

Weeks at No. 1, Title, Artist, Year Reached No. 1
20, "The Bodyguard" (soundtrack), Whitney Houston, 1992

15, "Tapestry," Carole King, 1971
14, "Whitney Houston," Whitney Houston, 1986
14, "Judy at Carnegie Hall," Judy Garland, 1961
13, "Jagged Little Pill," Alanis Morissette, 1995
11, "Fearless," Taylor Swift, 2008
11, "Mariah Carey," Mariah Carey, 1991
11, "Whitney," Whitney Houston, 1987
10, "Forever Your Girl," Paula Abdul, 1989
10, "The Singing Nun," the Singing Nun, 1963
9, "21," Adele, 2011
9, "Pearl," Janis Joplin, 1971

With its ninth week atop the Billboard 200, "21" additionally passes the Beatles' "1" for second-longest reign for a solely-numerical title. Among such sets, only Foreigner's "4" led longer (10 weeks, 1981).

Here is a ranking of the eight sets (including Roman numerals and even a prior "21"), ranked by most weeks spent at No. 1, from "1" to "5150":

Weeks at No. 1, Title, Artist, Year Reached No. 1
10, "4," Foreigner, 1981
9, "21," Adele, 2011
8, "1," the Beatles, 2000
5, "II," Boyz II Men, 1994
3, "5150," Van Halen, 1986
1, "21," Omarion, 2007
1, "IV," Godsmack, 2006
1, "3121," Prince, 2006


HOW SWEET IT IS: The cinema classic "Pure Imagination" graces the Billboard Hot 100 for the first time, as the "Glee" cast's cover of the song from the 1971 film "Willy Wonka & the Chocolate Factory" enters at No. 59.

The Fox TV troupe debuts two additional songs - "Back to Black" (No. 82) and "My Man" (No. 94) - extending its record to 151 charted titles since its arrival two years ago this week.

While "Imagination" makes its Hot 100 introduction, Michael Feinstein's interpretation of the song has charted on Jazz Digital Songs and Kid Digital Songs, while Mariah Carey released a remix of her 1999 No. 4 Hot 100 hit "I Still Believe" that incorporated the composition's melody.

(Click on Chart Beat's video diary of the recent Chiller Fest 2011 to find out if Michael Bollner, aka, the original "Augustus Gloop," is a real-life chocolate addict or if he only played one in the movie).