CREATE TABLE table_49531 ("Class" TEXT, "Wheel arrangement" TEXT, "Fleet number ( s ) " TEXT, "Manufacturer" TEXT, "Year made" TEXT, "Quantity made" TEXT, "Quantity preserved" TEXT)

Which fleet numbers has quantity of 1?
SELECT "Fleet number(s)" FROM table_49531 WHERE "Quantity made" = '1'
SELECT "Fleet number(s)" FROM "table_49531" WHERE "Quantity made" = '1'