21664305 ÷ 91 
The aim is to understand the frequency of 91 in 21664305.

Moving on to step 1:
When dividing 2 by 91, we get 0 with a remainder of 2.
Write down 0 as next digit of the result. 
Result so far: 0.0
The remainder is 2 after subtracting 0 from 2.
Take the next digit (1) from the dividend and append it to 2, then repeat: 21 / 91

Let's proceed to step 2:
91 can be fit into 21 0 times, resulting in a remainder of 21.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Subtracting 0 from 21 leaves us with 21.
Append the next digit (6) from the dividend to 21 and continue with: 216 / 91

Going ahead to step 3:
If we divide 216 by 91, we get 2 and a remainder of 34.
Write down 2 as next digit of the result. 
Result so far: 2.0
If we take 182 away from 216, we end up with 34.
Fetch the next digit (6) from the dividend, attach it to 34 and continue: 346 / 91

Advancing to step 4:
91 goes into 346 3 times with a remainder of 73.
Record the quotient 3 as the next digit in the result. 
Result so far: 23.0
The remainder is 73 after subtracting 273 from 346.
Grab the next digit (4) from the dividend, add it to 73, then carry on: 734 / 91

Moving on to step 5:
When dividing 734 by 91, we get 8 with a remainder of 6.
Put 8 as the next digit of the answer. 
Result so far: 238.0
Subtracting 728 from 734 leaves us with 6.
Append the next digit (3) from the dividend to 6 and continue with: 63 / 91

Moving on to step 6:
When dividing 63 by 91, we get 0 with a remainder of 63.
Use 0 as the next digit of our solution. 
Result so far: 2380.0
Deduct 0 from 63 and we're left with 63.
Bring next digit (0) of the dividend behind the 63 and repeat the process: 630 / 91

Going ahead to step 7:
The number 91 fits into 630 6 times, leaving a remainder of 84.
The next digit of our result is 6. 
Result so far: 23806.0
The remainder is 84 after subtracting 546 from 630.
Grab the next digit (5) from the dividend, add it to 84, then carry on: 845 / 91

Advancing to step 8:
When dividing 845 by 91, we get 9 with a remainder of 26.
Write down 9 as next digit of the result. 
Result so far: 238069.0
Subtracting 819 from 845 leaves us with 26.
Since there are no more digits in the dividend, we add a zero to the remainder making it 260, and continue the process.

On to step 9:
If we divide 260 by 91, we get 2 and a remainder of 78.
The number 2 becomes the next digit in our result. 
Result so far: 238069.2
If we take 182 away from 260, we end up with 78.
Since there are no more digits in the dividend, we add a zero to the remainder making it 780, and continue the process.

On to step 10:
780 divided by 91 is 8 with a remainder of 52.
Use 8 as the next digit of our solution. 
Result so far: 238069.28
The remainder is 52 after subtracting 728 from 780.
Since there are no more digits in the dividend, we add a zero to the remainder making it 520, and continue the process.

Advancing to step 11:
91 can be fit into 520 5 times, resulting in a remainder of 65.
Put 5 as the next digit of the answer. 
Result so far: 238069.285
Subtracting 455 from 520 leaves us with 65.
Since there are no more digits in the dividend, we add a zero to the remainder making it 650, and continue the process.

Moving on to step 12:
650 divided by 91 is 7 with a remainder of 13.
Record the quotient 7 as the next digit in the result. 
Result so far: 238069.2857
The remainder is 13 after subtracting 637 from 650.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

Let's proceed to step 13:
91 goes into 130 1 times with a remainder of 39.
The next digit of our result is 1. 
Result so far: 238069.28571
Deduct 91 from 130 and we're left with 39.
Since there are no more digits in the dividend, we add a zero to the remainder making it 390, and continue the process.

Let's proceed to step 14:
If we divide 390 by 91, we get 4 and a remainder of 26.
The number 4 becomes the next digit in our result. 
Result so far: 238069.285714
If we take 364 away from 390, we end up with 26.
Since there are no more digits in the dividend, we add a zero to the remainder making it 260, and continue the process.

On to step 15:
91 goes into 260 2 times with a remainder of 78.
Record the quotient 2 as the next digit in the result. 
Result so far: 238069.2857142
If we take 182 away from 260, we end up with 78.
Since there are no more digits in the dividend, we add a zero to the remainder making it 780, and continue the process.

On to step 16:
The number 91 fits into 780 8 times, leaving a remainder of 52.
The next digit of our result is 8. 
Result so far: 238069.28571428
Subtracting 728 from 780 leaves us with 52.
Since there are no more digits in the dividend, we add a zero to the remainder making it 520, and continue the process.

The final outcome is 238069.28571428, with a leftover of 5.2e-08.