Number Series - General Questions

Look at this series: 51, 56, 61, 66, 71, 76, … What number should come next?

Look at this series and find the number that does not belong: 5, 5, 9, 15, 25, 40, 65

Look at this series: 47, 53, 59, 61, 67, 71, … What number should come next?

Look at this series: 3, 83, 7, 81, 11, 79, … What number should come next?

Look at this series: 4, 6, 9, 13, 18, 24, … What number should come next?