You can display 'Week numbers' from Android Ver.4.5.4.
The week containing January 1st is the first week of the year and is numbered week 1.
The week numbers will display on 'Monthly' calendar and 'Weekly' Calendar.
To display week numbers:
-Open side mene
-Tap 'App Settings'
-Tap 'Week Numbers'
Currently, Week Numbers is available only on the Android.
Relevant:Change of start day