We look at the division of 689581 by 21 
The aim is to understand the frequency of 21 in 689581.

On to step 1:
If we divide 6 by 21, we get 0 and a remainder of 6.
Use 0 as the next digit of our solution. 
Result so far: 0.0
If we subtract 0 from 6, we get 6.
Take the next digit (8) from the dividend and append it to 6, then repeat: 68 / 21

Let's proceed to step 2:
The number 21 fits into 68 3 times, leaving a remainder of 5.
Record the quotient 3 as the next digit in the result. 
Result so far: 3.0
Subtract 63 from 68 to get 5.
Take the next digit (9) from the dividend and append it to 5, then repeat: 59 / 21

Going ahead to step 3:
When dividing 59 by 21, we get 2 with a remainder of 17.
The next digit of our result is 2. 
Result so far: 32.0
Deduct 42 from 59 and we're left with 17.
Fetch the next digit (5) from the dividend, attach it to 17 and continue: 175 / 21

On to step 4:
175 divided by 21 is 8 with a remainder of 7.
Record the quotient 8 as the next digit in the result. 
Result so far: 328.0
The remainder is 7 after subtracting 168 from 175.
Take the next digit (8) from the dividend and append it to 7, then repeat: 78 / 21

Step 5:
21 goes into 78 3 times with a remainder of 15.
Record the quotient 3 as the next digit in the result. 
Result so far: 3283.0
If we subtract 63 from 78, we get 15.
Take the next digit (1) from the dividend and append it to 15, then repeat: 151 / 21

Going ahead to step 6:
21 goes into 151 7 times with a remainder of 4.
Use 7 as the next digit of our solution. 
Result so far: 32837.0
If we subtract 147 from 151, we 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.

Let's proceed to step 7:
21 goes into 40 1 times with a remainder of 19.
Record the quotient 1 as the next digit in the result. 
Result so far: 32837.1
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.

Let's proceed to step 8:
21 can be fit into 190 9 times, resulting in a remainder of 1.
The next digit of our result is 9. 
Result so far: 32837.19
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.

Advancing to step 9:
10 divided by 21 is 0 with a remainder of 10.
The next digit of our result is 0. 
Result so far: 32837.19
If we take 0 away from 10, 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.

Moving on to step 10:
When dividing 100 by 21, we get 4 with a remainder of 16.
The number 4 becomes the next digit in our result. 
Result so far: 32837.1904
Subtract 84 from 100 to get 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

Step 11:
21 goes into 160 7 times with a remainder of 13.
Use 7 as the next digit of our solution. 
Result so far: 32837.19047
Subtracting 147 from 160 leaves us 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.

Advancing to step 12:
If we divide 130 by 21, we get 6 and a remainder of 4.
Put 6 as the next digit of the answer. 
Result so far: 32837.190476
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.

On to step 13:
The number 21 fits into 40 1 times, leaving a remainder of 19.
Put 1 as the next digit of the answer. 
Result so far: 32837.1904761
Subtract 21 from 40 to get 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Let's proceed to step 14:
190 divided by 21 is 9 with a remainder of 1.
Use 9 as the next digit of our solution. 
Result so far: 32837.19047619
Subtracting 189 from 190 leaves us with 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

The final result is 32837.19047619 with a remainder of 1e-09.