We're dividing 51237011 by 399 
The aim is to understand the frequency of 399 in 51237011.

Advancing to step 1:
399 goes into 5 0 times with a remainder of 5.
The next digit of our result is 0. 
Result so far: 0.0
If we take 0 away from 5, we end up with 5.
Include the next digit (1) from the dividend after 5, then repeat: 51 / 399

Step 2:
If we divide 51 by 399, we get 0 and a remainder of 51.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Subtracting 0 from 51 leaves us with 51.
Include the next digit (2) from the dividend after 51, then repeat: 512 / 399

Moving on to step 3:
The number 399 fits into 512 1 times, leaving a remainder of 113.
The next digit of our result is 1. 
Result so far: 1.0
If we subtract 399 from 512, we get 113.
Bring next digit (3) of the dividend behind the 113 and repeat the process: 1133 / 399

Advancing to step 4:
If we divide 1133 by 399, we get 2 and a remainder of 335.
The next digit of our result is 2. 
Result so far: 12.0
Deduct 798 from 1133 and we're left with 335.
Grab the next digit (7) from the dividend, add it to 335, then carry on: 3357 / 399

On to step 5:
399 goes into 3357 8 times with a remainder of 165.
The next digit of our result is 8. 
Result so far: 128.0
The remainder is 165 after subtracting 3192 from 3357.
Fetch the next digit (0) from the dividend, attach it to 165 and continue: 1650 / 399

Let's proceed to step 6:
When dividing 1650 by 399, we get 4 with a remainder of 54.
The number 4 becomes the next digit in our result. 
Result so far: 1284.0
If we subtract 1596 from 1650, we get 54.
Fetch the next digit (1) from the dividend, attach it to 54 and continue: 541 / 399

On to step 7:
399 goes into 541 1 times with a remainder of 142.
The number 1 becomes the next digit in our result. 
Result so far: 12841.0
Subtracting 399 from 541 leaves us with 142.
Append the next digit (1) from the dividend to 142 and continue with: 1421 / 399

Moving on to step 8:
When dividing 1421 by 399, we get 3 with a remainder of 224.
Put 3 as the next digit of the answer. 
Result so far: 128413.0
Subtracting 1197 from 1421 leaves us with 224.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2240, and continue the process.

Moving on to step 9:
When dividing 2240 by 399, we get 5 with a remainder of 245.
Put 5 as the next digit of the answer. 
Result so far: 128413.5
If we take 1995 away from 2240, we end up with 245.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2450, and continue the process.

On to step 10:
When dividing 2450 by 399, we get 6 with a remainder of 56.
Write down 6 as next digit of the result. 
Result so far: 128413.56
The remainder is 56 after subtracting 2394 from 2450.
Since there are no more digits in the dividend, we add a zero to the remainder making it 560, and continue the process.

Let's proceed to step 11:
If we divide 560 by 399, we get 1 and a remainder of 161.
The next digit of our result is 1. 
Result so far: 128413.561
If we subtract 399 from 560, we get 161.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1610, and continue the process.

Advancing to step 12:
If we divide 1610 by 399, we get 4 and a remainder of 14.
Put 4 as the next digit of the answer. 
Result so far: 128413.5614
The remainder is 14 after subtracting 1596 from 1610.
Since there are no more digits in the dividend, we add a zero to the remainder making it 140, and continue the process.

Moving on to step 13:
140 divided by 399 is 0 with a remainder of 140.
The number 0 becomes the next digit in our result. 
Result so far: 128413.5614
If we subtract 0 from 140, we get 140.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1400, and continue the process.

Going ahead to step 14:
399 can be fit into 1400 3 times, resulting in a remainder of 203.
Put 3 as the next digit of the answer. 
Result so far: 128413.561403
The remainder is 203 after subtracting 1197 from 1400.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2030, and continue the process.

Advancing to step 15:
399 can be fit into 2030 5 times, resulting in a remainder of 35.
Put 5 as the next digit of the answer. 
Result so far: 128413.5614035
Subtracting 1995 from 2030 leaves us with 35.
Since there are no more digits in the dividend, we add a zero to the remainder making it 350, and continue the process.

Step 16:
399 goes into 350 0 times with a remainder of 350.
Write down 0 as next digit of the result. 
Result so far: 128413.5614035
If we subtract 0 from 350, we get 350.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3500, and continue the process.

The final result is 128413.5614035 with a remainder of 3.5e-07.