19.
Ten.
43
If you mean: 9, 19, 39, 69 then the next number in the sequence is 109
23 Prime numbers are odd numbers and 21=3x7
After 19 comes 20. In the base-10 numbering system, numbers are organized in a sequential order from 0 to 9, and then the next number is formed by adding a digit in the tens place and resetting the units place to 0. So, after 19 (which is composed of 1 in the tens place and 9 in the units place), the next number is 20 (with 2 in the tens place and 0 in the units place).
31
35
19.
Ten.
67
43
If you mean: 9, 19, 39, 69 then the next number in the sequence is 109
27
27
23 Prime numbers are odd numbers and 21=3x7
Crib! I haven't played in decades. The number 19 comes to mind, but it was so long ago. not played for awhile but it is 19