We look at the division of 121264 by 21 
The aim is to understand the frequency of 21 in 121264.

Advancing to step 1:
If we divide 1 by 21, we get 0 and a remainder of 1.
Write down 0 as next digit of the result. 
Result so far: 0.0
If we take 0 away from 1, we end up with 1.
Take the next digit (2) from the dividend and append it to 1, then repeat: 12 / 21

Moving on to step 2:
21 can be fit into 12 0 times, resulting in a remainder of 12.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Subtract 0 from 12 to get 12.
Bring next digit (1) of the dividend behind the 12 and repeat the process: 121 / 21

Advancing to step 3:
21 can be fit into 121 5 times, resulting in a remainder of 16.
Write down 5 as next digit of the result. 
Result so far: 5.0
The remainder is 16 after subtracting 105 from 121.
Include the next digit (2) from the dividend after 16, then repeat: 162 / 21

Advancing to step 4:
21 can be fit into 162 7 times, resulting in a remainder of 15.
Write down 7 as next digit of the result. 
Result so far: 57.0
If we subtract 147 from 162, we get 15.
Take the next digit (6) from the dividend and append it to 15, then repeat: 156 / 21

Let's proceed to step 5:
21 goes into 156 7 times with a remainder of 9.
Put 7 as the next digit of the answer. 
Result so far: 577.0
Deduct 147 from 156 and we're left with 9.
Take the next digit (4) from the dividend and append it to 9, then repeat: 94 / 21

Going ahead to step 6:
21 can be fit into 94 4 times, resulting in a remainder of 10.
The next digit of our result is 4. 
Result so far: 5774.0
The remainder is 10 after subtracting 84 from 94.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Step 7:
If we divide 100 by 21, we get 4 and a remainder of 16.
The number 4 becomes the next digit in our result. 
Result so far: 5774.4
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.

Let's proceed to step 8:
The number 21 fits into 160 7 times, leaving a remainder of 13.
The number 7 becomes the next digit in our result. 
Result so far: 5774.47
Deduct 147 from 160 and we're left 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 9:
130 divided by 21 is 6 with a remainder of 4.
Record the quotient 6 as the next digit in the result. 
Result so far: 5774.476
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.

Going ahead to step 10:
21 goes into 40 1 times with a remainder of 19.
The next digit of our result is 1. 
Result so far: 5774.4761
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.

Going ahead to step 11:
When dividing 190 by 21, we get 9 with a remainder of 1.
The next digit of our result is 9. 
Result so far: 5774.47619
Deduct 189 from 190 and we're left 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.

Let's proceed to step 12:
10 divided by 21 is 0 with a remainder of 10.
Use 0 as the next digit of our solution. 
Result so far: 5774.47619
Subtract 0 from 10 to get 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Going ahead to step 13:
21 can be fit into 100 4 times, resulting in a remainder of 16.
Record the quotient 4 as the next digit in the result. 
Result so far: 5774.4761904
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.

Let's proceed to step 14:
The number 21 fits into 160 7 times, leaving a remainder of 13.
The number 7 becomes the next digit in our result. 
Result so far: 5774.47619047
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.

The final outcome is 5774.47619047, with a leftover of 1.3e-08.