We divide 851410 by 21
The aim is to understand the frequency of 21 in 851410.

Advancing to step 1:
The number 21 fits into 8 0 times, leaving a remainder of 8.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
Subtracting 0 from 8 leaves us with 8.
Fetch the next digit (5) from the dividend, attach it to 8 and continue: 85 / 21

Step 2:
85 divided by 21 is 4 with a remainder of 1.
The next digit of our result is 4. 
Result so far: 4.0
If we subtract 84 from 85, we get 1.
Append the next digit (1) from the dividend to 1 and continue with: 11 / 21

Step 3:
11 divided by 21 is 0 with a remainder of 11.
Use 0 as the next digit of our solution. 
Result so far: 40.0
If we take 0 away from 11, we end up with 11.
Take the next digit (4) from the dividend and append it to 11, then repeat: 114 / 21

Let's proceed to step 4:
The number 21 fits into 114 5 times, leaving a remainder of 9.
Use 5 as the next digit of our solution. 
Result so far: 405.0
Subtracting 105 from 114 leaves us with 9.
Grab the next digit (1) from the dividend, add it to 9, then carry on: 91 / 21

Let's proceed to step 5:
When dividing 91 by 21, we get 4 with a remainder of 7.
Put 4 as the next digit of the answer. 
Result so far: 4054.0
If we subtract 84 from 91, we get 7.
Take the next digit (0) from the dividend and append it to 7, then repeat: 70 / 21

Step 6:
21 can be fit into 70 3 times, resulting in a remainder of 7.
Use 3 as the next digit of our solution. 
Result so far: 40543.0
If we subtract 63 from 70, we get 7.
Since there are no more digits in the dividend, we add a zero to the remainder making it 70, and continue the process.

Let's proceed to step 7:
If we divide 70 by 21, we get 3 and a remainder of 7.
The number 3 becomes the next digit in our result. 
Result so far: 40543.3
The remainder is 7 after subtracting 63 from 70.
Since there are no more digits in the dividend, we add a zero to the remainder making it 70, and continue the process.

Let's proceed to step 8:
21 goes into 70 3 times with a remainder of 7.
The next digit of our result is 3. 
Result so far: 40543.33
Subtract 63 from 70 to get 7.
Since there are no more digits in the dividend, we add a zero to the remainder making it 70, and continue the process.

After the division, we end up with 40543.33 and a remainder of 0.007.