Electron Configuration (chemistry)?

obviously 6 comes from the period number with the s and p orbitals. The d orbitals start and 3 and end at 6. so what is considered the 4th period for the d orbital is the 3rd. The s orbital can only hold a maximum of 4 electrons, the d orbital 20 and the p orbital 6. Two electrons occupy each orbital, therefore there are 2s orbitals, 10 d orbitals, and 3 p orbitals. This rule was made in accordance to the layout of the periodic table. if you can just remember that d orbitals are always one level behind you can get it!! good luck.