# Claudio Cherubino's blogLife of a Googler

4Feb/080

## Project Euler in F# – Problem 16

This time we are gonna "cheat".

As in Problem 20 we have to sum the digits of a number, so we can just copy and paste the whole code and edit a single line to have a working solution.

The problem says:

2^15 = 32768 and the sum of its digits is 3 + 2 + 7 + 6 + 8 = 26.

What is the sum of the digits of the number 2^1000?

The only difference between this exercise and the last one is the number to evaluate.

However, as for the factorial, F# already provides us with a native function for the powers of a numbers, so the final code will be:

```#light
open Microsoft.FSharp.Math.BigInt

let rec digits n =
match n with
| n when n < 10I -> n
| n ->
let x, y = divmod n 10I
y + digits x

let answer = digits (pow 2I 1000I)
```

If you compare this exercise with the last one, you can see that we actually changed one line, i.e. line 11.

Do you really want me to explain this code?

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