Define N(n, Ic) as the number of permutations of n absolute values of residuals yielding k peaks. For convenience we define N(l, 0) = 1. We make the obser- vation that adjoining an nth residual to n- 1 others can create a total of k peaks in two ways: (i) if the preceding n- 1 residuals yielded k peaks and the last one creates no new one, and (ii) if the preceding n - 1 residuals yielded k - 1 peaks and the ith one does create an additional peak. This yields the following recursions