Wednesday
September 13th 1961 was a Wednesday.
Dec 13th 1961 was a Wednesday.
Tuesday
Friday
Saturday
It was Friday.
From a perpetual US calendar: September 13, 1960 was on Tuesday.
13th September 1962 was a Thursday.
September 13th, 1987, was a Sunday.
September 13th, 1971 fell on a Monday.
September 13th, 1981 fell on a Sunday.
November 13th 1961 was a Monday.