CREATE TABLE table_203_27 (id DECIMAL, "number" DECIMAL, "serial no" DECIMAL, "entered service" TEXT, "withdrawn" TEXT, "kilometres travelled" DECIMAL)

what was the next locomotive to be withdrawn after locomotive 4106
SELECT "number" FROM table_203_27 WHERE "withdrawn" > (SELECT "withdrawn" FROM table_203_27 WHERE "number" = 4106) ORDER BY "withdrawn" LIMIT 1
SELECT "number" FROM "table_203_27" WHERE "withdrawn" > (SELECT "withdrawn" FROM "table_203_27" WHERE "number" = 4106) ORDER BY "withdrawn" NULLS FIRST LIMIT 1