Not sure the effect you're really after but
set(gca,'YTick',[1 2 4 8 16 18])
which can be
set(gca,'YTick',[2.^[0:4] 18])
if you're looking for more concise formulation for the values.
If you intend the ticks to be spaced evenly but labeled otherwise, have to use N (in this case 6) tick values spaced as desired and then 'xticklabel' to write the desired label value at the respective location.
