When I last wrote about HOOD stock in August, I noted that Robinhood had already shown that it knows very well how to attract millennials. I cited Cestrian Capital Research, which stated in an Aug. 20 column that Robinhood had attracted many millennials with "its simple app and website, modern user interface and focus on accounts with relatively small balances." Robinhood also became popular by allowing investors to buy and sell cryptocurrencies.