Card counting is a very simple system that anyone can learn, so the it does not require a notebook filled with equations as shown.
When Charlie, Larry, and Amita are doing their "research" at the Bicycle Casino, you can hear the faint sounds of slot machines in the background. The Bicycle Casino does not have slot machines. It is a card club.
When Larry first sees the notebook filled with equations, he looks puzzled and studies the notebook before Don takes it back to make copies. He says there is something vaguely familiar about them. Later he tells Charlie and Almeda he recognized the equations immediately when he saw them which was not the case based on the way he reacted previously.
To expose an addict to his addiction is highly unethical and way out of character for Charlie, especially considering Larry is his best friend.