Perfect month

A perfect month or a rectangular month designates a month whose number of days is divisible by the number of days in a week and whose first day corresponds to the first day of the week.
The arrangement of the days of the month in the calendar then forms a rectangle.
Constraints.
To satisfy such a arrangement in the Gregorian calendar, the number of days in the month must be divisible by seven. Therefore, only the month of February of a non-leap year can meet this constraint. Thus, January 1 must be a Friday.
Occurrence.
In the Gregorian calendar, the phenomenon occurs every 6 years or 11 years following a 6-11-11 sequence until the end of the 21st century. The last perfect month was February 2021.
Attributes.
The calendar arrangement brings together notions of harmony and organization.