Counting

When we are walking together (with Nathan holding mommy and daddy's hands) we will count 1-2-3 and then swing him. Nathan seems to have figured this out so whenever we walk he says "twooo, threeee" and then stops walking. Because of this we have discovered he is trying to figure out how to count. He rarely ever says one, but if we say one he will say two, three. Then if we say four he will say five. He will then repeat 6-10 back to us as we say them (sometimes he says a few of them without being prompted). I tried to get this on video today but he wouldn't cooperate.