Try this:

Create a Named formula, by going to Insert|Name|Define.

Call it "Range" (without quotes) and use formula: 

=INDEX(Sheet1!$D$13:$D$1000,1+((ROW(Sheet1!$B1)-1)*3)):INDEX(Sheet1!$D$13:$D$1000,505+((ROW(Sheet1!$B1)-1)*3))
where 1000 defines the furthest down you will need to sum in range column D.

then apply formula in spreadsheet:

=SUM(IF(ISNUMBER(Range),IF((MOD(ROW(Range)-ROW($D13),36)=0)*(Range),Range)))
Confirmed with CTRL+SHIFT+ENTER not just ENTER and then copy down.