Your formula can be simplified to 0.

Your inner IF returns an array with FALSE in every row except where
there is a 17 in A1:A999 (where it returns 17). Since there are no 13's
in the array produced by the inner IF, the outer IF returns an array of
999 FALSE values; therefore SUM returns zero.

Jerry

Andrew < wrote:

Hey Guys,

Is there a special name for this kind of formula?

=SUM(IF(A1:A999=13,IF(A1:A999=17,A1:A999)))

I was pretending to work yesterday and came up with it as a
multicriteria alternative to Filters.

If nobody can prove prior credit, I hereby name it a Nested SumIf
Array! (Hey, I'm just a newbie, gimme a break)