CREATE TABLE table_18541 ("District" CLOB, "Incumbent" CLOB, "Party" CLOB, "First elected" FLOAT, "Result" CLOB, "Candidates" CLOB)

What is the number of candidates for pennsylvania 21
SELECT COUNT("Candidates") FROM table_18541 WHERE "District" = 'Pennsylvania 21'
SELECT COUNT("Candidates") FROM "table_18541" WHERE "District" = 'Pennsylvania 21'