Find the missing number in the sequence.
4, 10, 40, 190, 940, ?, 23440
4690
2930
5140
3680
None of these
56, 42, ?, 20, 12, 6, 2
2, 8, 18, 32, 50, 72, (?)
20, 19, 17, __ , 10, 5
996, 1000, 992, 1004, 988, ?, 984
1, 2, 3, 5, 8, __, 21