SymPy Gamma

Input:

rsolve(y(n+2)-y(n+1)-y(n), y(n))

Error:

rsolve(y(n+2)-y(n+1)-y(n), y(n))

unsupported operand type(s) for *: 'UndefinedFunction' and 'Add'

See what Wolfram|Alpha has to say.

Experiment with SymPy at SymPy Live.