Larkin is from the Irish Ó Lorcáin — from Irish lorcán (fierce/cruel) — also possibly little rough one. Larkin is one of the Irish-English feminine + unisex names — central to traditional English literary heritage.
Larkin 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 Larkin reduce to 2, The Peacemaker. This is a traditional interpretive system, not a factual claim about the name.