250592 ÷ 21 
The aim is to understand the frequency of 21 in 250592.

Step 1:
21 can be fit into 2 0 times, resulting in a remainder of 2.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Subtract 0 from 2 to get 2.
Append the next digit (5) from the dividend to 2 and continue with: 25 / 21

Moving on to step 2:
If we divide 25 by 21, we get 1 and a remainder of 4.
The next digit of our result is 1. 
Result so far: 1.0
Deduct 21 from 25 and we're left with 4.
Take the next digit (0) from the dividend and append it to 4, then repeat: 40 / 21

Step 3:
When dividing 40 by 21, we get 1 with a remainder of 19.
Use 1 as the next digit of our solution. 
Result so far: 11.0
Deduct 21 from 40 and we're left with 19.
Append the next digit (5) from the dividend to 19 and continue with: 195 / 21

Advancing to step 4:
If we divide 195 by 21, we get 9 and a remainder of 6.
The next digit of our result is 9. 
Result so far: 119.0
Deduct 189 from 195 and we're left with 6.
Append the next digit (9) from the dividend to 6 and continue with: 69 / 21

Advancing to step 5:
21 goes into 69 3 times with a remainder of 6.
The number 3 becomes the next digit in our result. 
Result so far: 1193.0
The remainder is 6 after subtracting 63 from 69.
Fetch the next digit (2) from the dividend, attach it to 6 and continue: 62 / 21

Advancing to step 6:
The number 21 fits into 62 2 times, leaving a remainder of 20.
The number 2 becomes the next digit in our result. 
Result so far: 11932.0
Subtracting 42 from 62 leaves us with 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Moving on to step 7:
21 can be fit into 200 9 times, resulting in a remainder of 11.
Write down 9 as next digit of the result. 
Result so far: 11932.9
The remainder is 11 after subtracting 189 from 200.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

On to step 8:
21 goes into 110 5 times with a remainder of 5.
Write down 5 as next digit of the result. 
Result so far: 11932.95
Subtract 105 from 110 to get 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

On to step 9:
50 divided by 21 is 2 with a remainder of 8.
Write down 2 as next digit of the result. 
Result so far: 11932.952
Subtracting 42 from 50 leaves us with 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Moving on to step 10:
If we divide 80 by 21, we get 3 and a remainder of 17.
Use 3 as the next digit of our solution. 
Result so far: 11932.9523
If we subtract 63 from 80, we get 17.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

Advancing to step 11:
170 divided by 21 is 8 with a remainder of 2.
Put 8 as the next digit of the answer. 
Result so far: 11932.95238
If we take 168 away from 170, we end up with 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

Going ahead to step 12:
If we divide 20 by 21, we get 0 and a remainder of 20.
Write down 0 as next digit of the result. 
Result so far: 11932.95238
The remainder is 20 after subtracting 0 from 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

On to step 13:
21 can be fit into 200 9 times, resulting in a remainder of 11.
Write down 9 as next digit of the result. 
Result so far: 11932.9523809
If we take 189 away from 200, we end up with 11.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

Going ahead to step 14:
The number 21 fits into 110 5 times, leaving a remainder of 5.
Record the quotient 5 as the next digit in the result. 
Result so far: 11932.95238095
The remainder is 5 after subtracting 105 from 110.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

The final outcome is 11932.95238095, with a leftover of 5e-09.