21666 ÷ 9 = 2407 R3
Let's divide 21666 by 9.

Step 1:
9 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 / 9

Step 2:
9 goes into 21 2 times with a remainder of 3.
Write down 2 as next digit of of the result. 
Result so far: 2
Subtract 18 from 21 to get 3.
Bring next digit (6) of the dividend behind the 3 and repeat the process: 36 / 9

Step 3:
9 goes into 36 4 times with a remainder of 0.
Write down 4 as next digit of of the result. 
Result so far: 24
Subtract 36 from 36 to get 0.
Bring next digit (6) of the dividend behind the 0 and repeat the process: 6 / 9

Step 4:
9 goes into 6 0 times with a remainder of 6.
Write down 0 as next digit of of the result. 
Result so far: 240
Subtract 0 from 6 to get 6.
Bring next digit (6) of the dividend behind the 6 and repeat the process: 66 / 9

Step 5:
9 goes into 66 7 times with a remainder of 3.
Write down 7 as next digit of of the result. 
Result so far: 2407
Subtract 63 from 66 to get 3.

The final result is 2407 with a remainder of 3.