Runing Sum Filter

running sum m- query  The Code

( ) as list =>
let
pList = {1,2,3,4,5,6,7,8,9} ,
runSum=List.Generate(
()=>[ xx =0 , zz=pList{0} ],
each [xx] <=List.Count(pList) ,
each [ xx=[xx]+1 , zz = [zz] + pList{ [xx]+1 } ] , each [zz]
)
in
runSum

 the output will be {1,3,6,10,15,21,28 ...}

on filtering the list on index value >3

i have to start from  values {4,9,15,22...}

insted of {10,15,21,28}

it to work like ranking that recreate the index from start  or dax exp 

  ???