Mamie is a 19th-century American diminutive of Mary or Margaret — popularized as a pet name in the late 1800s. Mamie Eisenhower (1896-1979) — wife of Dwight D.
Mamie 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 Mamie reduce to 5, The Seeker. This is a traditional interpretive system, not a factual claim about the name.