371200 ÷ 21 
The aim is to understand the frequency of 21 in 371200.

On to step 1:
21 can be fit into 3 0 times, resulting in a remainder of 3.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Subtract 0 from 3 to get 3.
Append the next digit (7) from the dividend to 3 and continue with: 37 / 21

Moving on to step 2:
21 can be fit into 37 1 times, resulting in a remainder of 16.
The number 1 becomes the next digit in our result. 
Result so far: 1.0
Subtract 21 from 37 to get 16.
Grab the next digit (1) from the dividend, add it to 16, then carry on: 161 / 21

Advancing to step 3:
21 can be fit into 161 7 times, resulting in a remainder of 14.
Use 7 as the next digit of our solution. 
Result so far: 17.0
The remainder is 14 after subtracting 147 from 161.
Include the next digit (2) from the dividend after 14, then repeat: 142 / 21

Let's proceed to step 4:
142 divided by 21 is 6 with a remainder of 16.
Record the quotient 6 as the next digit in the result. 
Result so far: 176.0
Deduct 126 from 142 and we're left with 16.
Take the next digit (0) from the dividend and append it to 16, then repeat: 160 / 21

Moving on to step 5:
21 can be fit into 160 7 times, resulting in a remainder of 13.
Record the quotient 7 as the next digit in the result. 
Result so far: 1767.0
Subtracting 147 from 160 leaves us with 13.
Fetch the next digit (0) from the dividend, attach it to 13 and continue: 130 / 21

Step 6:
When dividing 130 by 21, we get 6 with a remainder of 4.
The next digit of our result is 6. 
Result so far: 17676.0
The remainder is 4 after subtracting 126 from 130.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

Moving on to step 7:
40 divided by 21 is 1 with a remainder of 19.
Put 1 as the next digit of the answer. 
Result so far: 17676.1
If we take 21 away from 40, we end up with 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Step 8:
If we divide 190 by 21, we get 9 and a remainder of 1.
Write down 9 as next digit of the result. 
Result so far: 17676.19
The remainder is 1 after subtracting 189 from 190.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Advancing to step 9:
21 goes into 10 0 times with a remainder of 10.
Write down 0 as next digit of the result. 
Result so far: 17676.19
Subtract 0 from 10 to get 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

On to step 10:
21 goes into 100 4 times with a remainder of 16.
The next digit of our result is 4. 
Result so far: 17676.1904
Deduct 84 from 100 and we're left with 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

On to step 11:
160 divided by 21 is 7 with a remainder of 13.
Record the quotient 7 as the next digit in the result. 
Result so far: 17676.19047
The remainder is 13 after subtracting 147 from 160.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

Step 12:
When dividing 130 by 21, we get 6 with a remainder of 4.
The number 6 becomes the next digit in our result. 
Result so far: 17676.190476
The remainder is 4 after subtracting 126 from 130.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

Advancing to step 13:
If we divide 40 by 21, we get 1 and a remainder of 19.
The number 1 becomes the next digit in our result. 
Result so far: 17676.1904761
The remainder is 19 after subtracting 21 from 40.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

On to step 14:
When dividing 190 by 21, we get 9 with a remainder of 1.
The number 9 becomes the next digit in our result. 
Result so far: 17676.19047619
The remainder is 1 after subtracting 189 from 190.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

After the division, we end up with 17676.19047619 and a remainder of 1e-09.