This site explains how to calculate in your head (in often less than one second) the day of the week for any calendar date. It also explains how to calculate the day, month or year when one of those other elements of a date is unknown but the day of the week is known. There is no faster or simpler formula out there.
X13 March 15, 44 B.C.
Aha, another trick question. Of course, we all know from our history books that March 15, 44 B.C. was the Ides of March, the day Julius Cesar was killed. while I guess you could make some backward translation of the Gregorian calendar to the Roman calendar, the one that was in us at the time of Ceasar's death, why bother? That does not interest me so I will not go through my own translation here.