Excel, how to increment row number for the SUM function? -

Excel, how to increment row number for the SUM function? -

i have excel spreadsheet original info in range a1:a100

i want cell b1 sum of a1:a5, b2 = sum(a6:a10), b3 = sum(a11:a15) , on. formula can utilize cell b1, allow me re-create others b cells accomplish above?

thanks , regards, nhan.

=sum(offset(a1,4*(row(a1)-1),,5))

excel