Folks,
What it comes down to is that some people count ingredients and some people do not. Both are operating within the tradition of African American folk magic and neither is more right, correct, educated, or "powerful" than the other.
Then, among those who count ingredients, certain numbers may be preferred. Most common are 3, 4, 5, 7, and 13 -- and there are reasons for all, as Mary described above.
4: For more on the link between the Native American use of the number 4 and its connection to African American hoodoo root doctors, see this 19th century account of a jack ball made by 4s, as described by Mary Alicia Owen at this "Southern Spiritrs" web page:
Hoodoo Luck Balls (Jack Balls) by Mary Alicia Owen
http://southern-spirits.com/owen-hoodoo-luck-balls.html
5: For more on the 5-spot or quincunx pattern, see the potion of this page at "Hoodoo in Theory and Practice" that describes the quincunx and its uses:
Laying Down Tricks and Disposing of Ritual Remains in the Hoodoo Tradition
http://luckymojo.com/layingtricks.html#quincunx
7: For more on the number 7, including the old hoodoo formula called "Japanese Lucky 7 Oil," see this "Lucky W Amulet Archive" page:
Lucky Number Seven
http://www.luckymojo.com/number7.html
13: For more on the lucky number 13 and Lucky Mojo Lucky 13 spiritual supplies, see this "Hoodoo in Theory and Practice" page:
Lucky 13 Spiritual Supplies in Hoodoo Rootwork
http://www.luckymojo.com/lucky13.html