Hcg doubling fast

Manda • Baby #1 March 10, 2016. Baby #2 November 1, 2017.
I know you can't tell if you're having twins from hcg levels, but I'm curious to see if any of you had hcg levels that doubled faster than the 48-72 hr norm. My first at 4w2d (based on lmp) was 473. I wasn't able to go back until a week later at 5w2d and it was 11,478. An hcg calculator online said it's doubling every 1.5 days or about every 36 hours. Just curious!