@ snb
of course no need for indirect but if the worksheet has other calx's
=MATCH(15,SQRT(ROW(A1:A1000))+SQRT(ROW(A1:A1000)+15),0)
to reduce the volatile recalculation to column A
other array formula variations

I thought you more an index dude
=MATCH(15,SQRT(ROW(INDEX(A:A,1):INDEX(A:A,1000))+15)+SQRT(ROW(INDEX(A:A,1):INDEX(A:A,1000))),1)
or
=MATCH(15,SQRT(ROW(OFFSET(A1,,,1000))+15)+SQRT(ROW(OFFSET(A1,,,1000))),1)