Look at this series: 8, 6, 9, 23, 87 , ... What number should come next?

Look at this series: 1.5, 2.3, 3.1, 3.9, ... What number should come next?

Look at this series: 21, 9, 21, 11, 21, 13, 21, ... What number should come next?

Look at this series: 31, 29, 24, 22, 17, ... What number should come next?

Look at this series: 544, 509, 474, 439, ... What number should come next?

Look at this series: 22, 21, 23, 22, 24, 23, ... What number should come next?

Look at this series: 2, 4, 6, 8, 10, ... What number should come next?

Look at this series: 58, 52, 46, 40, 34, ... What number should come next?