Brain Teasers and Puzzles 

Workings

Hint

Answer
1680.

This is n to the power of 5, starting with 2^5 = 32, with the last digit missing, 7^5 = 16807.

Workings

Hint

Answer
293 031: these are the numbers 20, 21, 22, 23 etc grouped into three digits.

Workings

Hint
The sequence is related to 1, 2, 3, 4.

Answer
20.

Each term's initial letter position in the alphabet:

1 = One = O = 15^th letter.
.
.
4 = Four = F = 6^th letter.
.
.
.
20 = Ten = T = 20^th letter.

Workings

Hint
The sequence involves both adding and multiplying in some way.

Answer
153.

The sequence is created using: +1 x1 +2 x2 +3 x3 +4 x4 +5.