20451 ÷ 6 = 3408 R3
Alright, let's work through the division of 20451 by 6 step by step.

Step 1:
6 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 (0) of the dividend behind the 2 and repeat the process: 20 / 6

Step 2:
6 goes into 20 3 times with a remainder of 2.
Write down 3 as next digit of of the result. 
Result so far: 3
Subtract 18 from 20 to get 2.
Bring next digit (4) of the dividend behind the 2 and repeat the process: 24 / 6

Step 3:
6 goes into 24 4 times with a remainder of 0.
Write down 4 as next digit of of the result. 
Result so far: 34
Subtract 24 from 24 to get 0.
Bring next digit (5) of the dividend behind the 0 and repeat the process: 5 / 6

Step 4:
6 goes into 5 0 times with a remainder of 5.
Write down 0 as next digit of of the result. 
Result so far: 340
Subtract 0 from 5 to get 5.
Bring next digit (1) of the dividend behind the 5 and repeat the process: 51 / 6

Step 5:
6 goes into 51 8 times with a remainder of 3.
Write down 8 as next digit of of the result. 
Result so far: 3408
Subtract 48 from 51 to get 3.

The final result is 3408 with a remainder of 3.