Sunday.
September 20th, 1981 was a Sunday.
20th September 1974 was a Friday.
20th September 2010 was a Monday.
September 20th, 1961 fell on a Wednesday.
September 7 1981 was a Monday.
September 24 1981 was a Thursday.
It was a Tuesday.
It was a Friday.
August 20th, 1981 was a Thursday.
November 20th, 1981 fell on a Friday.
September 4, 1981 fell on a Friday.
September 6, 1981 fell on a Sunday.