big o – Big-O notation of a function that grows exponentially

I have a library that finds out the the values of Pi up to a given number.

It takes 10x the time to calculate 3n than it takes to calculate n.

For example,

  • For 1000 digits it takes 0.012 seconds
  • For 3000 digits it takes 0.116 seconds
  • For 9000 digits it takes 1.161 seconds
  • For 27000 digits it takes 11.614 seconds
  • For 81000 digits it takes 116.14 seconds
  • For 243000 digits it takes 1161.4 seconds
  • For 729000 digits it takes 11614.002 seconds
  • For 2187000 digits it takes 116140.02 seconds
  • For 6561000 digits it takes 1161400.2 seconds
  • For 19683000 digits it takes 11614002.0 seconds

I have personally tried numbers up to 243,000, which really agrees with the calculation as well.

So, what will be the Big-O notation of this algorithm?