We look at the division of 690388 by 21 
The aim is to understand the frequency of 21 in 690388.

Moving on to step 1:
21 goes into 6 0 times with a remainder of 6.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Deduct 0 from 6 and we're left with 6.
Fetch the next digit (9) from the dividend, attach it to 6 and continue: 69 / 21

Moving on to step 2:
The number 21 fits into 69 3 times, leaving a remainder of 6.
Write down 3 as next digit of the result. 
Result so far: 3.0
Deduct 63 from 69 and we're left with 6.
Append the next digit (0) from the dividend to 6 and continue with: 60 / 21

Advancing to step 3:
21 goes into 60 2 times with a remainder of 18.
Use 2 as the next digit of our solution. 
Result so far: 32.0
Deduct 42 from 60 and we're left with 18.
Append the next digit (3) from the dividend to 18 and continue with: 183 / 21

Step 4:
183 divided by 21 is 8 with a remainder of 15.
Write down 8 as next digit of the result. 
Result so far: 328.0
Subtracting 168 from 183 leaves us with 15.
Grab the next digit (8) from the dividend, add it to 15, then carry on: 158 / 21

Moving on to step 5:
If we divide 158 by 21, we get 7 and a remainder of 11.
Put 7 as the next digit of the answer. 
Result so far: 3287.0
Subtracting 147 from 158 leaves us with 11.
Take the next digit (8) from the dividend and append it to 11, then repeat: 118 / 21

Advancing to step 6:
The number 21 fits into 118 5 times, leaving a remainder of 13.
The number 5 becomes the next digit in our result. 
Result so far: 32875.0
Subtracting 105 from 118 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.

Step 7:
21 goes into 130 6 times with a remainder of 4.
Put 6 as the next digit of the answer. 
Result so far: 32875.6
Subtracting 126 from 130 leaves us with 4.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

Going ahead to step 8:
The number 21 fits into 40 1 times, leaving a remainder of 19.
Record the quotient 1 as the next digit in the result. 
Result so far: 32875.61
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.

On to step 9:
190 divided by 21 is 9 with a remainder of 1.
Record the quotient 9 as the next digit in the result. 
Result so far: 32875.619
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.

Step 10:
The number 21 fits into 10 0 times, leaving a remainder of 10.
Record the quotient 0 as the next digit in the result. 
Result so far: 32875.619
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.

Let's proceed to step 11:
The number 21 fits into 100 4 times, leaving a remainder of 16.
The next digit of our result is 4. 
Result so far: 32875.61904
If we subtract 84 from 100, we 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 12:
160 divided by 21 is 7 with a remainder of 13.
The next digit of our result is 7. 
Result so far: 32875.619047
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.

Advancing to step 13:
If we divide 130 by 21, we get 6 and a remainder of 4.
The next digit of our result is 6. 
Result so far: 32875.6190476
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 14:
The number 21 fits into 40 1 times, leaving a remainder of 19.
The next digit of our result is 1. 
Result so far: 32875.61904761
If we subtract 21 from 40, we 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.

After the division, we end up with 32875.61904761 and a remainder of 1.9e-08.