There can only be ten, not nine and not eleven.

In Section 1:4 of the Sefer Yetzirah it reads:
Ten Sefirot of Nothingness
ten and not nine
ten and not eleven.

So what gets counted as part of the ten?
Obviously Hokhmah, Binah, Hesed, Gedulah, Gevurah, Tifereth, Netzach, Hod, and Yesod are all part of the ten. But this only gets you eight.  Which get counted as the ninth and the tenth.
Here is where it gets interesting.
Some commentators say that Keter is so much a part of Ayn Sof that it can't be considered part of the ten and thus Malkuth and Da'at, get added into the mix to make up the ten.
But, the GRA had an interesting other idea.  His view was hinted at in the picture that Aryeh Kaplan put on the cover of his translation and commentary to the Sefer Yetzirah.  That same image was figure 6 on page 31.  There it is referenced as "The paths defined by the Gra, as they appear in the Warsaw, 1884 edition, (p. 26b of Part Two)."
That is where we see what appears to be the array Kaplan calls the 'natural array'.  He even presents what he thinks is the way to interpret that figure of the GRA's on page 30 of Kaplan's book, which he calls the "32 paths according to the Gra".  Only Kaplan made a mistake and misinterpreted the GRA's diagram.  The so called 'natural array' excludes Malkuth which hangs on a slender line below Yesod.  Thus the ten consists of the upper active portion of the Divine powers, and Malkuth is outside of this system and outside of this counting.  To make the numbers come to ten, once more Da'at has to be in the mix.
I posted on this blog site that essay which explains how I derived this conclusion.  
In that essay I quote from the commentary by the GRA to the Sefer Yetzirah in which he explains why Malkuth is excluded and thus Da'at is included.