A Slow Relative of Hofstadter's Q-Sequence
  Hofstadter's Q-sequence remains an enigma fifty years after its introduction. Initially, the terms of the sequence increase monotonically by 0 or 1 at a time. But, Q(12)=8 while Q(11)=6, and monotonicity fails shortly thereafter. In this paper, we add a third term to Hofstadter's recurrence, giving the recurrence B(n)=B(n-B(n-1))+B(n-B(n-2))+B(n-B(n-3)). We show that this recurrence, along with a suitable initial condition that naturally generalizes Hofstadter's initial condition, generates a sequence whose terms all increase monotonically by 0 or 1 at a time. Furthermore, we give a complete description of the resulting frequency sequence, which allows the nth term of our sequence to be efficiently computed. We conclude by showing that our sequence cannot be easily generalized. 
Nathan Fox
math.NT math.CO