Which Worksheet Functions can return an Array

If I have a list of 20 dates in column A like:

12/5/2015
8/8/2000
4/26/2002
2/13/2009
1/29/2013
7/25/2004
8/21/2002
11/8/2010
11/13/2006
5/1/2002
2/11/2012
9/7/2010
4/12/2012
10/29/2011
4/29/2004
11/27/2003
11/10/2002
9/30/2005
9/24/2001
6/20/2002

I can count how many of the are in 2002 with this:

=SUMPRODUCT(--(YEAR(A$1:A$20)=2002))

If I try to count how many have weeknumber 46 with this:

=SUMPRODUCT(--(WEEKNUM(A$1:A$20)=46))

I get #VALUE!

Many years ago I asked why and was told:

"As everyone knows, WEEKNUM() does not return an array and so cannot be used in SUMPRODUCT() in that way."

The phrase As everyone knows really bugged me. I wanted to know what everyone else knows, so I tried to find an online reference that listed which functions can return an array and which cannot.

Can anyone help me find an online reference for this information ??

Functions that were in Analysis ToolPak in Excel 2003 (like WEEKNUM, WORKDAY and NETWORKDAYS among others) don't accept range arguments, but they do accept arrays.

So, if you use =SUMPRODUCT(--(WEEKNUM(A$1:A$20+0)=46)), it will work. Adding a +0 makes the range into an array.