The DeMark indicators are a $500 per month third-party package available by subscription on Bloomberg.
I would be overjoyed if someone came up with a Combo AFL for AmiBroker.
Regarding interpretation, I suggest Tom Demark's books "The New Science of Technical Analysis", "DeMark on Day Trading Options" and Jason Perl's "DeMark Indicators". You can find them on Amazon.
The Sequential indicator is just one of DeMark's studies. It is not a system. However, it is useful in finding points of exhaustion that have an above average chance of a price reversal. Simplistically, a 9-count creates a Setup from which you look for a 1 to 4 bar retracement. If the Setup took out a previous TDST level (now 6077 in NIFTY) the chances are good that the trend will continue after the pullback. From there, two versions of a 13-countdown are possible; Sequential and Combo. A 'price flip' after a 13-countdown confirms the reversal. The Shanghai Comp, Hang Seng and ASX all generated 13's on June 24, around the bottom. The Nifty bottom in August was choppier, but never closed below the risk levels of 5089 and 5032.