## Hints
For this exercise the following F# feature comes in handy:
- [BigInt](https://msdn.microsoft.com/en-us/visualfsharpdocs/conceptual/numerics.biginteger-structure-%5Bfsharp%5D)
- [Seq.sumBy](https://msdn.microsoft.com/en-us/visualfsharpdocs/conceptual/seq.sumby%5B't,%5Eu%5D-function-%5Bfsharp%5D) is a condensed format to apply a function to a sequence and then sum the results