#[05AB1E](http://github.com/Adriandmen/05AB1E), [4 bytes, Paul Picard](https://codegolf.stackexchange.com/a/77443/34388), [A001317](https://oeis.org/A001317) Code: $Fx^ [Try it online!](http://05ab1e.tryitonline.net/#code=JEZ4Xg&input=OA) Explanation: $ # Pushes 1 and input F # Pops x, creates a for-loop in range(0, x) x # Pops x, pushes x and 2x ^ # Bitwise XOR on the last two elements # Implicit, ends the for-loop # Implicit, nothing has printed so the last element is printed automatically The sequence basically is a binary Sierpinski triangle: f(0)= 1 =1 f(1)= 1 1 =3 f(2)= 1 0 1 =5 f(3)= 1 1 1 1 =15 f(4)= 1 0 0 0 1 =17 And translates to the formula **a(n) = a(n - 1) XOR (2 × a(n - 1))** Luckily, I remembered [this one](https://codegolf.stackexchange.com/a/67503/34388) :)