Wellllll..... not JUST 6, but the 6 that do not usually fall on a Sunday are:

~January 1—Mary, Mother of God
~40th day after Easter—Ascension of our Lord
  (only obligation for CT,MA,NY,NJ,NE,PA)      
~August 15—Assumption of the Blessed Virgin Mary
~November 1—All Saints
~December 8—Immaculate Conception
~December 25—Nativity of Our Lord Jesus Christ

Can you guess what the other 52 Holy Days of Obligation are? 
That's correct! EVERY Sunday (or Saturday Vigial)