This may help you for sure -
note down numbers series 1 4 7 ...drag it further to automatically fill it.
above it, use formula - =MID($B$2,B5,3) and drag it further to copy it automatically.
see image 1
Image 1:
Now,
Copy the data and paste it in values and transpose it.
then use the below formula - left, mid & right as shown in image 2.
Image 2:
This will atleast make your work easier. Please let me know if i can help you further.
Thanks,
Praveen