42639 ÷ 2 = 21319 R1
Alright, let's work through the division of 42639 by 2 step by step.

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

Step 2:
2 goes into 2 1 times with a remainder of 0.
Write down 1 as next digit of of the result. 
Result so far: 21
Subtract 2 from 2 to get 0.
Bring next digit (6) of the dividend behind the 0 and repeat the process: 6 / 2

Step 3:
2 goes into 6 3 times with a remainder of 0.
Write down 3 as next digit of of the result. 
Result so far: 213
Subtract 6 from 6 to get 0.
Bring next digit (3) of the dividend behind the 0 and repeat the process: 3 / 2

Step 4:
2 goes into 3 1 times with a remainder of 1.
Write down 1 as next digit of of the result. 
Result so far: 2131
Subtract 2 from 3 to get 1.
Bring next digit (9) of the dividend behind the 1 and repeat the process: 19 / 2

Step 5:
2 goes into 19 9 times with a remainder of 1.
Write down 9 as next digit of of the result. 
Result so far: 21319
Subtract 18 from 19 to get 1.

The final result is 21319 with a remainder of 1.