hi, Werner !

... 4 sheets... "sheet1", "sheet2", "sheet3", "sheet4"
... sheet1!A1=1, sheet2!A1=2, sheet3!A1=3.
sheet4!A1=sheet1, sheet4!B1=sheet2, sheet4!C1=sheet3.
sheet4!A2="=INDIRECT(A1 & "!A1")"
sheet4!B2="=INDIRECT(B1 & "!A1")"
sheet4!C2="=INDIRECT(C1 & "!A1")"
This works and I get the right results.
When I try an array formula on sheet4 like {=INDIRECT(A1:C1 & "!A1")} I get "#VALUE!".
The formula is placed in three horizontal cells and I have entered it with Ctrl+Shift+Enter.
When I calculate a part of the formula... I get the arrays, which I have expected, but at the end it doesn't work.

FWIW, if you use a range-array, you have to indicate which index from the array goes into each cell
try again with: =index(indirect(a1:c1&"!a1"),{1;2;3})
[placed in three horizontal cells and entered with ctrl+shift+enter]

hth,
hector.