SymPy Gamma logo SymPy Gamma

rsolve (y(n+2)-y(n+1)-y(n),y(n),{y(0):0,y(1):1})
2**(-n)*sqrt(5)*((1 + sqrt(5))**n - (-sqrt(5) + 1)**n)/5
See what Wolfram|Alpha has to say.

Experiment with SymPy at SymPy Live.