memoized factorial for bc

bc on solaris craps out with recursion when the level's over 48

define f(x) {
  if (x>1) {
    if (f[x]) {
      return (f[x])
    }
    f[x] = (x * f(x-1))
    return (f[x])
  }
  return (1)
}

memoization partly fixes the annoyance.