Question: How many annual indicators use the Sum aggregation method from 2001 to 2003?
SQL: SELECT COUNT(DISTINCT T2.SeriesCode)  FROM Footnotes AS T1 INNER JOIN Series AS T2 ON T1.Seriescode = T2.SeriesCode WHERE T1.Year IN ('YR2001', 'YR2002', 'YR2003') AND T2.Periodicity = 'Annual' AND T2.AggregationMethod = 'Sum'