Let's divide 15980196 by 399
The aim is to understand the frequency of 399 in 15980196.

Going ahead to step 1:
399 can be fit into 1 0 times, resulting in a remainder of 1.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Deduct 0 from 1 and we're left with 1.
Bring next digit (5) of the dividend behind the 1 and repeat the process: 15 / 399

Going ahead to step 2:
15 divided by 399 is 0 with a remainder of 15.
Write down 0 as next digit of the result. 
Result so far: 0.0
Subtracting 0 from 15 leaves us with 15.
Grab the next digit (9) from the dividend, add it to 15, then carry on: 159 / 399

Advancing to step 3:
The number 399 fits into 159 0 times, leaving a remainder of 159.
The next digit of our result is 0. 
Result so far: 0.0
Deduct 0 from 159 and we're left with 159.
Take the next digit (8) from the dividend and append it to 159, then repeat: 1598 / 399

Moving on to step 4:
When dividing 1598 by 399, we get 4 with a remainder of 2.
Put 4 as the next digit of the answer. 
Result so far: 4.0
Deduct 1596 from 1598 and we're left with 2.
Append the next digit (0) from the dividend to 2 and continue with: 20 / 399

Moving on to step 5:
The number 399 fits into 20 0 times, leaving a remainder of 20.
The next digit of our result is 0. 
Result so far: 40.0
Subtracting 0 from 20 leaves us with 20.
Fetch the next digit (1) from the dividend, attach it to 20 and continue: 201 / 399

Step 6:
399 can be fit into 201 0 times, resulting in a remainder of 201.
Use 0 as the next digit of our solution. 
Result so far: 400.0
If we subtract 0 from 201, we get 201.
Take the next digit (9) from the dividend and append it to 201, then repeat: 2019 / 399

Advancing to step 7:
When dividing 2019 by 399, we get 5 with a remainder of 24.
Use 5 as the next digit of our solution. 
Result so far: 4005.0
Subtract 1995 from 2019 to get 24.
Append the next digit (6) from the dividend to 24 and continue with: 246 / 399

Let's proceed to step 8:
399 can be fit into 246 0 times, resulting in a remainder of 246.
Write down 0 as next digit of the result. 
Result so far: 40050.0
If we subtract 0 from 246, we get 246.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2460, and continue the process.

Advancing to step 9:
The number 399 fits into 2460 6 times, leaving a remainder of 66.
The number 6 becomes the next digit in our result. 
Result so far: 40050.6
Subtracting 2394 from 2460 leaves us with 66.
Since there are no more digits in the dividend, we add a zero to the remainder making it 660, and continue the process.

Step 10:
The number 399 fits into 660 1 times, leaving a remainder of 261.
Write down 1 as next digit of the result. 
Result so far: 40050.61
Subtract 399 from 660 to get 261.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2610, and continue the process.

Advancing to step 11:
If we divide 2610 by 399, we get 6 and a remainder of 216.
The next digit of our result is 6. 
Result so far: 40050.616
If we take 2394 away from 2610, we end up with 216.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2160, and continue the process.

Moving on to step 12:
The number 399 fits into 2160 5 times, leaving a remainder of 165.
The next digit of our result is 5. 
Result so far: 40050.6165
Deduct 1995 from 2160 and we're left with 165.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1650, and continue the process.

Going ahead to step 13:
399 goes into 1650 4 times with a remainder of 54.
Put 4 as the next digit of the answer. 
Result so far: 40050.61654
If we subtract 1596 from 1650, we get 54.
Since there are no more digits in the dividend, we add a zero to the remainder making it 540, and continue the process.

Going ahead to step 14:
When dividing 540 by 399, we get 1 with a remainder of 141.
Put 1 as the next digit of the answer. 
Result so far: 40050.616541
Deduct 399 from 540 and we're left with 141.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1410, and continue the process.

Step 15:
When dividing 1410 by 399, we get 3 with a remainder of 213.
The next digit of our result is 3. 
Result so far: 40050.6165413
If we subtract 1197 from 1410, we get 213.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2130, and continue the process.

Advancing to step 16:
399 goes into 2130 5 times with a remainder of 135.
The next digit of our result is 5. 
Result so far: 40050.61654135
Subtract 1995 from 2130 to get 135.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1350, and continue the process.

The final outcome is 40050.61654135, with a leftover of 1.35e-07.