How many art products were ordered in 2013 in the east superstore?
ordered in 2013 refers to strftime('%Y', "Order Date") = '2013'; art products refers to "Sub-Category" = 'Art'
SELECT COUNT(DISTINCT T1.`Product ID`) FROM east_superstore AS T1 INNER JOIN product AS T2 ON T1.`Product ID` = T2.`Product ID` WHERE T2.`Sub-Category` = 'Art' AND T1.Region = 'East' AND STRFTIME('%Y', T1.`Order Date`) = '2013'