Continue number sequence

Can someone help with this?

I have attached a book in case I haven't explained well enough.

I want to continue the number sequence in column A so that it matches the results in column D.

In range A1:A8 are the numbers 1 to 8, then there are 4 blanks and then 1 in A13.
I have thousands of rows of blanks to do manually so was hoping for some formula that I could drag down in column B.
The numbers are always consecutive and all the blanks are above he value of 1.

Thanks