How to group time to YM(year/month, 1st half moth and 2nd half month, for example, 20200401 means 1st half month and 20200402 means the second month.
Here is a formula that produces the Character String as you you requested
Char( Year( :Full Date ) ) || Char( Month( :Full Date ) ) ||
If( Day( :Full Date ) >= 15,
If you need a numeric value, I would simply precede the entire formula with Num ("formula")