I would like to use indirect instead of :

=sum(Sheet2!:Sheet5!:b10)

however even just typing in the text does not work

=sum(indirect("Sheet2!:Sheet5!:b10"))

putting Sheet names within ''s also doesn't seem to work.

=sum(indirect("'Sheet2'!:'Sheet5'!:b10"))

a1="Sheet2"

a2="Sheet5"

=sum(indirect(a1$&"!:"&a2&"!:b10"))

If you have a solution that would work on Sheet2!A7:Sheet5!:b10 that would be great.

I believe that I have tried dozens of variations of double and single quotes. If anyone can help, thanks,

Thanks in advance.