I wanted to see what could be done with the Fibonacci sequence, but I didn’t have something that played nicely with LINQ. Here is my first cut:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 

Then you can do all sorts of computations.
1 2 3 4 

But why BigInteger? When using int, the 46th Fibonacci number is the last capable of being represented; making the data type a uint gets us the 47th. When using long, the 92nd is the last with the and with ulong the 93rd. With the BigInteger implementation, I can generate the 250,000th in about four seconds! And I can go much higher. If .NET had shipped with a BigFloat class I would have tried using the closed form solution which we could use to calculate the series in parallel. Having to sort may negate the speedup, but any solutions that don’t require order might benefit well.
There is another problem with using BigInteger; I can’t return a BigFloat from an .Average() calculation and BigInteger doesn’t support any kind of fraction support other than modulo. I wonder how much work it would be to create a BogFloat based on BigInteger.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 
