Number Series - General Questions

Look at this series: 121, 117, 113, 109, 105, 101, … What number should come next?

Look at this series and find the number that does not belong: 1, 8, 27, 67, 125, 216, 343

Look at this series: 146, 137, 128, 119, 110, 101, … What number should come next?

Look at this series: 143, 133, 123, 113, 103, 93, … What number should come next?

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