Riddles and brain teasing questions

[21 Savage]

Hey everyone,this game is something I created a while ago. The idea is that the first person says a riddle or brain teasing question as he desires and others give answers. The person with the correct answer gets to give another riddle for the thread and he must give a reason for the answer. I will begin with this riddle. : what digits should appear after this list of numbers- 4 5 6 6 5 4 4 2