It's a sixteenth triplet, followed by one tied regular eighth note. The little 3 is placed clearly between the sixteenth note of the triplet and the following tied eighth, which contains the other two triplet sixteenths. The following eighth note (which is tied as well) counts as a regular eighth note.
I think my approach to learning this would be to think in sixteenth triplets throughout the whole first measure, and the respective other measures. So you have three sixteenths in the triplet, three triplet sixteenths in the following eighth note and six triplet sixteenths in the following (also tied) quarter note. And of course 12 triplet sixteenths in the underlying half note.
The lack of the triplet 3 later on reads as "simile", it's all the same rhythm (ostinato pattern).
In measure 3 (and 18, and 19) you need to think two of these triplet sixteenths in each eighth note of the triplet in the right hand, to get it correctly together.