About seedwords expand

[EricLingRui]

Thanks for the article, it inspired me a lot！I have a question about seedwords expand ... When I see the code :

n1 = 5
n = min(n1 * (it), int(math.log(len(label_docs_dict[index_to_label[l]]), 1.5)))

There seems to be no explanation in the paper,I want to know why it is set up in this way.