Template:Weekdate2orddate

[expression "7*{{{2}}}+{{{3}}}-7+(700000006 - 2006 - (((2006-1)/4 -0.499) round 0) + (2006>=250) * ( 5 + (((2006-1)/100 -0.499) round 0) - ((2006-1)/400 -0.499) round 0)) mod 7 - 3" in start week 1 gives system message ""]

2 Sunday 2006-01-01, week 0, ordinal date 1, MJD = 53736.

For ISO 8601 year-week-day of week, find ordinal date in the Gregorian year.