=SUMPRODUCT(--(MOD(ROW(A1:A20),2)=1),A1:A20)

gets A1,A3, etc.

To get A2,A4, etc. then change =1 to =0.

For every third, do a MOD(...,3)

etc.

--

HTH

RP

"Brent" wrote in message
...
Hello,

I have a need to sum the values in every other cell, and sometimes every
third cell, in a column or row.

Thanks
--
Brent