Very hard IQ induction based problem (Stuck for over 30 mins)

[light yagami]

 

Hi guys, I would greatly appreciate the solution to this...

For some context and familiarity, the puzzles are usually pattern spotting based and continuing it.

Also, I must add that I've gathered an 'obvious' solution to this that seems to fit in but is not the correct answer, that being '2332' (according to the rules of entering the answer).

http://peconinja.web.fc2.com/777e/CDE.html

or

[Thalia]

I tried entering a number on a whim to see what would happen. It seems to have taken it. Is it normal to get an error message if you type the wrong answer?

1221. I couldn't tell you why. It seems to fit a pattern if you ignore the 5th set but with it included, I can't explain it.

[NT!]

Answer is 1221
It's a Pyramid and  2>1>3