The Delhi Sultanate period is indeed from 1206-1526 AD. It began with Qutb-ud-din Aibak's establishment of the Slave dynasty in 1206 and ended with the fall of the Ibrahim Lodi in 1526 to Babar in the First Battle of Panipat. This approximately 320-year period saw five dynasties: Slave (Mamluk), Khilji, Tughlaq, Sayyid, and Lodi.