Why won't Wolfram|Alpha accept this input?

{f[n] == ((Sum[f[a]^(a-n), {a, 1, n-1}]) + 1), f[1] == 1, f[10]}

Even though all of my syntax is correct (as far as I can tell), it only returns this message:

Try the following:


  • Use different phrasing or notations
  • Enter whole words instead of abbreviations
  • Avoid mixing mathematical and other notations
  • Check your spelling
  • Give your input in English

Any help would be appreciated, thanks!