We look at the division of 51821664 by 210 
The aim is to understand the frequency of 210 in 51821664.

Let's proceed to step 1:
5 divided by 210 is 0 with a remainder of 5.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Subtracting 0 from 5 leaves us with 5.
Append the next digit (1) from the dividend to 5 and continue with: 51 / 210

On to step 2:
The number 210 fits into 51 0 times, leaving a remainder of 51.
Write down 0 as next digit of the result. 
Result so far: 0.0
The remainder is 51 after subtracting 0 from 51.
Grab the next digit (8) from the dividend, add it to 51, then carry on: 518 / 210

Going ahead to step 3:
When dividing 518 by 210, we get 2 with a remainder of 98.
The next digit of our result is 2. 
Result so far: 2.0
If we take 420 away from 518, we end up with 98.
Grab the next digit (2) from the dividend, add it to 98, then carry on: 982 / 210

On to step 4:
210 goes into 982 4 times with a remainder of 142.
The next digit of our result is 4. 
Result so far: 24.0
The remainder is 142 after subtracting 840 from 982.
Append the next digit (1) from the dividend to 142 and continue with: 1421 / 210

Step 5:
The number 210 fits into 1421 6 times, leaving a remainder of 161.
The next digit of our result is 6. 
Result so far: 246.0
The remainder is 161 after subtracting 1260 from 1421.
Fetch the next digit (6) from the dividend, attach it to 161 and continue: 1616 / 210

Going ahead to step 6:
210 can be fit into 1616 7 times, resulting in a remainder of 146.
Record the quotient 7 as the next digit in the result. 
Result so far: 2467.0
Deduct 1470 from 1616 and we're left with 146.
Bring next digit (6) of the dividend behind the 146 and repeat the process: 1466 / 210

Moving on to step 7:
210 goes into 1466 6 times with a remainder of 206.
Write down 6 as next digit of the result. 
Result so far: 24676.0
Subtract 1260 from 1466 to get 206.
Include the next digit (4) from the dividend after 206, then repeat: 2064 / 210

Let's proceed to step 8:
2064 divided by 210 is 9 with a remainder of 174.
Write down 9 as next digit of the result. 
Result so far: 246769.0
Subtracting 1890 from 2064 leaves us with 174.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1740, and continue the process.

Step 9:
If we divide 1740 by 210, we get 8 and a remainder of 60.
The number 8 becomes the next digit in our result. 
Result so far: 246769.8
If we take 1680 away from 1740, we end up with 60.
Since there are no more digits in the dividend, we add a zero to the remainder making it 600, and continue the process.

Going ahead to step 10:
The number 210 fits into 600 2 times, leaving a remainder of 180.
Record the quotient 2 as the next digit in the result. 
Result so far: 246769.82
If we subtract 420 from 600, we get 180.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1800, and continue the process.

Advancing to step 11:
1800 divided by 210 is 8 with a remainder of 120.
The number 8 becomes the next digit in our result. 
Result so far: 246769.828
If we take 1680 away from 1800, we end up with 120.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1200, and continue the process.

Advancing to step 12:
The number 210 fits into 1200 5 times, leaving a remainder of 150.
The next digit of our result is 5. 
Result so far: 246769.8285
Subtract 1050 from 1200 to get 150.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1500, and continue the process.

Advancing to step 13:
If we divide 1500 by 210, we get 7 and a remainder of 30.
Put 7 as the next digit of the answer. 
Result so far: 246769.82857
The remainder is 30 after subtracting 1470 from 1500.
Since there are no more digits in the dividend, we add a zero to the remainder making it 300, and continue the process.

Going ahead to step 14:
When dividing 300 by 210, we get 1 with a remainder of 90.
The number 1 becomes the next digit in our result. 
Result so far: 246769.828571
Subtracting 210 from 300 leaves us with 90.
Since there are no more digits in the dividend, we add a zero to the remainder making it 900, and continue the process.

Going ahead to step 15:
210 goes into 900 4 times with a remainder of 60.
Use 4 as the next digit of our solution. 
Result so far: 246769.8285714
If we subtract 840 from 900, we get 60.
Since there are no more digits in the dividend, we add a zero to the remainder making it 600, and continue the process.

Let's proceed to step 16:
The number 210 fits into 600 2 times, leaving a remainder of 180.
Put 2 as the next digit of the answer. 
Result so far: 246769.82857142
If we subtract 420 from 600, we get 180.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1800, and continue the process.

The final outcome is 246769.82857142, with a leftover of 1.8e-07.