Random Puzzles 

Workings

Hint
The sequence is related to prime numbers.

Answer
29.

Each term increases by the next prime number.

Workings

Hint
Try starting with the cube root of the number.

Answer
195 x 197 x 199.

Reasoning
Since we're after three numbers that multiply together, a good place to start is the cube root of 7,644,585, which is roughly 196.99.

Let's try dividing by the closest odd number to 196.99:

   7644585 ÷ 197 = 38805

We're now after whole divisors of 38,805, so trying either odd number either side of 197 might work.

Trying either 195 or 199 gives the answer.

Double-Checking
   195 x 197 x 199 = 7,644,585

Note
Trying the closest odd number to the cube root always works, and the other two numbers are the odd numbers either side.

Workings

Hint
The first country is Bangladesh.

Answer
Bangladesh, Egypt, Fiji, Finland, Japan, Liechtenstein, Nicaragua, Switzerland, Tunisia, Zambia.

Workings

Hint
Try removing the spaces from the sequence.

Answer
1301311 or 1210121.

Reasoning
Removing spaces from the original sequence gives:

   1 23 124 1251 26127 128129

   123124125126127128129

Now adding spaces back in, in the correct place:

   123 124 125 126 127 128 129

The next few terms could be:

   130 131 132
   or
   1210 1211 1212

Add these to the end:

   123 124 125 126 127 128 129 130 131 132
   or
   123 124 125 126 127 128 129 1210 1211 1212

Remove the spaces again:

   123124125126127128129130131132
   or
   123124125126127128129121012111212

Now break the sequence into chunks of increasing size:

   1 23 124 1251 26127 128129 1301311
   or
   1 23 124 1251 26127 128129 1210121

So the missing term is 1301311 or 1210121.