src/Khayyam/Khayyam.php
public function endOfCentury()
     {
         return $this->endOfYear()->year($this->year - $this->year % static::YEARS_PER_CENTURY + static::YEARS_PER_CENTURY - 1);
     }
public function endOfCentury()
     {
         return $this->endOfYear()->year($this->year - $this->year % static::YEARS_PER_CENTURY + static::YEARS_PER_CENTURY - 1);
     }
Resets the date to end of the century and time to 23:59:59

@return static