Contemplating during meditation What can be object of contemplation during meditation? Can I take a puzzle or mathematical problem for contemplation? What is the right way of contemplation?
All this involve conceptualisation which can lead to delusional thoughts as with any mind constructed concept it is easy to lose sight of its true nature. This is called Vipallasa as discussed in Vipallasa Sutta.

Sometimes you cannot avoid doing intellectual work like a puzzle or mathematical work. This is not ideal, but any kind of mental activity or when you cognize you experience some sensation. (Titth’ayatana Sutta, Dhātu Vibhaṅga Sutta, etc.)

So if you are sensitive enough then perhaps you can try to look at the arising  and passing of these sensations with equanimity.



Some analysis from the Suttas.


  Cognizing a mental object with the mind, one examines the mental object as the basis for
  pleasure, or for pain, or for neither-pain-nor-pleasure


Source: Titth’ayatana Sutta. Hence the puzzle and math problem inevitably create some sensation which falls into the the 3 categories of either pleasant, painful or neither pleasant or painful. Similar passage appears in Dhātu Vibhaṅga Sutta also.


  If he wishes thus, ‘May I dwell rejecting both the unrepulsive and the repulsive, and dwell in
  equanimity, mindful and fully aware,’ he dwells therein equanimously, mindful and fully aware


Source: Indriya Bhāvanā Sutta. Clearly the math problem or puzzle is unrepulsive but you have to be equanimous when doing this.


  he dwells contemplating states that arise in the ... he dwells contemplating states that fall away in the ... he dwells contemplating states that arise and fall away in the ... he maintains this mindfulness: ‘There is ...’ just sufficient for knowing and awareness And he dwells independent, not clinging to anything in this world ...


Source: Mahā Satipatthāna Sutta. Here ... And he dwells independent, not clinging to anything in this world ... is equanimously, in your case not getting excited about the problem. ... just sufficient for knowing and awareness ... means there is no conceptualisation and though proliferation, which you your case is present but this has some sensation as previously discussed. If you are sensitive enough you can look at these sensations.