The Sound of Silence in Billboard Hot 100

How did the first hitsingle of Simon & Garfunkel 'behave' in the Billboard Hot 100? It entered the Hot 100 on the 21st of November on position 80 and moved upwards until January 1st of 1966 when it reached Nr. 1. But just for one week!
Then it went back to position 2 for the next two weeks. On January 21st it reached Nr. 1 once more. From then on it was 'down hill'........

BillBoard HOT 100
The Sound of Silence
Date Chart#
19651121 pos. 80
19651126 pos. 65
19651204 pos. 34
19651211 pos. 26
19651218 pos. 16
19651225 pos. 5
19660101 pos. 1
19660108 pos. 2
19660115 pos. 2
19660122 pos. 1
19660129 pos. 12
19660205 pos. 20