Fatou is from the Senegalese-Wolof rendition of Fatima — from the Arabic Fāṭimah (one who weans, abstains). Fatou is one of the Senegalese + Malian + Gambian + Mauritanian feminine names — central to traditional West African Muslim heritage devotion to Fatimah bint Muhammad.
Fatou does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
In Pythagorean numerology the letters of Fatou reduce to 9, The Giver. This is a traditional interpretive system, not a factual claim about the name.