This is a lemma 6 in published article called The Number of Prime Factors on Average in Certain Integer Sequences, page8. i have some trouble expounding or looking for the in between equation, before its came up to the second formula. Im not quite familiar with the notations that they using since it wasn't defined properly
example link, where u can view the article, retrieved from https://www.researchgate.net/publication/358229491_The_Number_of_Prime_Factors_on_Average_in_Certain_Integer_Sequences
