Help with Continuous Patterns in Non Sequential Cells

[leknuok]

I need help with creating a pattern with the average formula. I'm brand new to this site so I tried a search, but didn't have any luck finding what I wanted. This is the formula I'm currently using:

=IFERROR(AVERAGE(B19,B32,B45,B58,B71),"")

The IFERROR is for the cells that can't divide by 0 which I find works very nicely because the Average formula only takes in the numbers that actually exist.

My problem is that every week I add a new row of data. The pattern I have is essentially B+13 (I'm using cells B to AE) short of manually entering in the next cell, I'd like to know if there's a way to just have the formula do it for me automatically essentially to infinity.

 

[Asala42]

This array formula seems to test well:

{=AVERAGE(IF(($B$3:$B$1000<>0)*(MOD(ROW($B$3:$B$1000),13)=6),$B$3:$B$1000))}

Ctrl+Shift+Enter to get the brackets.