370807 ÷ 21 
The aim is to understand the frequency of 21 in 370807.

Advancing to step 1:
If we divide 3 by 21, we get 0 and a remainder of 3.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Deduct 0 from 3 and we're left with 3.
Bring next digit (7) of the dividend behind the 3 and repeat the process: 37 / 21

Going ahead to step 2:
21 can be fit into 37 1 times, resulting in a remainder of 16.
Write down 1 as next digit of the result. 
Result so far: 1.0
If we take 21 away from 37, we end up with 16.
Include the next digit (0) from the dividend after 16, then repeat: 160 / 21

Going ahead to step 3:
When dividing 160 by 21, we get 7 with a remainder of 13.
Put 7 as the next digit of the answer. 
Result so far: 17.0
Subtracting 147 from 160 leaves us with 13.
Fetch the next digit (8) from the dividend, attach it to 13 and continue: 138 / 21

Advancing to step 4:
21 can be fit into 138 6 times, resulting in a remainder of 12.
Write down 6 as next digit of the result. 
Result so far: 176.0
If we take 126 away from 138, we end up with 12.
Fetch the next digit (0) from the dividend, attach it to 12 and continue: 120 / 21

Going ahead to step 5:
When dividing 120 by 21, we get 5 with a remainder of 15.
The number 5 becomes the next digit in our result. 
Result so far: 1765.0
If we take 105 away from 120, we end up with 15.
Take the next digit (7) from the dividend and append it to 15, then repeat: 157 / 21

Advancing to step 6:
If we divide 157 by 21, we get 7 and a remainder of 10.
Use 7 as the next digit of our solution. 
Result so far: 17657.0
If we take 147 away from 157, we end up with 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Advancing to step 7:
100 divided by 21 is 4 with a remainder of 16.
Record the quotient 4 as the next digit in the result. 
Result so far: 17657.4
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 8:
If we divide 160 by 21, we get 7 and a remainder of 13.
The number 7 becomes the next digit in our result. 
Result so far: 17657.47
If we take 147 away from 160, we end up with 13.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

On to step 9:
If we divide 130 by 21, we get 6 and a remainder of 4.
Write down 6 as next digit of the result. 
Result so far: 17657.476
Subtract 126 from 130 to get 4.
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 10:
The number 21 fits into 40 1 times, leaving a remainder of 19.
The next digit of our result is 1. 
Result so far: 17657.4761
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.

Moving on to step 11:
21 goes into 190 9 times with a remainder of 1.
The next digit of our result is 9. 
Result so far: 17657.47619
If we subtract 189 from 190, we get 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Step 12:
The number 21 fits into 10 0 times, leaving a remainder of 10.
Write down 0 as next digit of the result. 
Result so far: 17657.47619
Deduct 0 from 10 and we're left with 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Let's proceed to step 13:
21 can be fit into 100 4 times, resulting in a remainder of 16.
Put 4 as the next digit of the answer. 
Result so far: 17657.4761904
If we take 84 away from 100, we end up 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.

Moving on to step 14:
When dividing 160 by 21, we get 7 with a remainder of 13.
Use 7 as the next digit of our solution. 
Result so far: 17657.47619047
Subtract 147 from 160 to get 13.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

Our division results in 17657.47619047 with a remaining 1.3e-08.