21404 ÷ 4 = 5351 R0
Alright, let's work through the division of 21404 by 4 step by step.

Step 1:
4 goes into 2 0 times with a remainder of 2.
Write down 0 as next digit of of the result. 
Result so far: 0
Subtract 0 from 2 to get 2.
Bring next digit (1) of the dividend behind the 2 and repeat the process: 21 / 4

Step 2:
4 goes into 21 5 times with a remainder of 1.
Write down 5 as next digit of of the result. 
Result so far: 5
Subtract 20 from 21 to get 1.
Bring next digit (4) of the dividend behind the 1 and repeat the process: 14 / 4

Step 3:
4 goes into 14 3 times with a remainder of 2.
Write down 3 as next digit of of the result. 
Result so far: 53
Subtract 12 from 14 to get 2.
Bring next digit (0) of the dividend behind the 2 and repeat the process: 20 / 4

Step 4:
4 goes into 20 5 times with a remainder of 0.
Write down 5 as next digit of of the result. 
Result so far: 535
Subtract 20 from 20 to get 0.
Bring next digit (4) of the dividend behind the 0 and repeat the process: 4 / 4

Step 5:
4 goes into 4 1 times with a remainder of 0.
Write down 1 as next digit of of the result. 
Result so far: 5351
Subtract 4 from 4 to get 0.

The final result is 5351 with a remainder of 0.