Gregorian - Monday-based month with weeks
  December 2147483646  
   Mo Tu We Th Fr Sa Su
48                 1  2
49  3  4  5  6  7  8  9
50 10 11 12 13 14 15 16
51 17 18 19 20 21 22 23
52 24 25 26 27 28 29 30
 1 31