Altan is from the Mongolian and Turkic altan / altın (golden, gold). Altan Köseoğlu — Turkish-American physicist. Princess Altan — Mongolian royal heritage. Altan Khan of Khalkha.
and Irish folk music.
Altan 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 Altan reduce to 3, The Communicator. This is a traditional interpretive system, not a factual claim about the name.