I have a table with three Columns: Column A: name of Item, Column B: Lowest value of series, Column C: the Highest value of series.

CodePudding user response：

try REDUCE:

=INDEX(QUERY(REDUCE(, A3:INDEX(A:A, MAX(ROW(A:A)*(A:A<>""))), 
 LAMBDA(x, a, {x; JOIN(, LAMBDA(i, f, u, i&"_"&SEQUENCE(1, u-f 1, f)&";")
 (a, OFFSET(a,,1), OFFSET(a,,2)))})), "offset 1", ))