66591 ÷ 4 = 16647 R3
We're going to perform division on 66591 with 4 as the divisor.

Step 1:
4 goes into 6 1 times with a remainder of 2.
Write down 1 as next digit of of the result. 
Result so far: 1
Subtract 4 from 6 to get 2.
Bring next digit (6) of the dividend behind the 2 and repeat the process: 26 / 4

Step 2:
4 goes into 26 6 times with a remainder of 2.
Write down 6 as next digit of of the result. 
Result so far: 16
Subtract 24 from 26 to get 2.
Bring next digit (5) of the dividend behind the 2 and repeat the process: 25 / 4

Step 3:
4 goes into 25 6 times with a remainder of 1.
Write down 6 as next digit of of the result. 
Result so far: 166
Subtract 24 from 25 to get 1.
Bring next digit (9) of the dividend behind the 1 and repeat the process: 19 / 4

Step 4:
4 goes into 19 4 times with a remainder of 3.
Write down 4 as next digit of of the result. 
Result so far: 1664
Subtract 16 from 19 to get 3.
Bring next digit (1) of the dividend behind the 3 and repeat the process: 31 / 4

Step 5:
4 goes into 31 7 times with a remainder of 3.
Write down 7 as next digit of of the result. 
Result so far: 16647
Subtract 28 from 31 to get 3.

The final result is 16647 with a remainder of 3.