THIS VIDEO TALKS ABOUT THE NUMBER SERIES:
LINK 1:   • NUMBER SERIES-PART-1 | PSYCHOLOGY | T...  
LINK 2:   • KOMAGATA MARU INCIDENT | MODERN HISTO...  
TYPES OF NUMBER SERIES:
1)n*3 series
2)n*3 +1 series
3) n*3 -1 series
4) n*3 + n series
5)n*3 - n series
6) alternating series
7) arithmetic progression
8) geometric progression.