How do you find the perimeter of an ellipse using maple?

For eg, x^2/20+y^2/13=1

Need help with starting this question. Thanks!

If a sequence is defined by X₀=0, X₁=1, X₂=2 and X_n=n(X_n-3+X_n-2+X_n-1), n>=3

How many digits will X₂₀₁₃ have?

I have no idea how to start to answer this question. Please help Thanks!

Let G(x) denote the no. of ways of representing n as the sum of two prime numbers.

For eg, G(10)=2: where 10=3+7=5+5

           G(20)=2: where 20=3+17=7+13

           G(30)=3: where 30=7+23=11+19=13+17

How do you find G(10 000 000)?

I'm having problem dealing with this question on Maple and would appreciate any help possible.

If f(x) = x/2, if x is even
   f(x) = 3x-1, if x is odd

which sequence will 2013^1102 fall in
1->1->1...
5->7->5...
17->25->37->55->41->61->91->17...

Thanks!