Problem #25

I use Mathematica for this. The original way I did it was with guess-and-check (e.g. is the 1000th one larger than it? no? how about the 5000th one? too large? ...). But, heres some Mathematica code that is a bit more efficient:

For[i = 0, 1000 > Length@IntegerDigits@Fibonacci@i, i++]; i