```
0 8 * * 6 test $((10#$(date +\%W)\%2)) -eq 1 && yourCommand
```

`date +%W`

: week number of year with Monday as first day of week, today week 39

`10#$(date +%W)`

: conver the `date +W`

to decimal number and avoid shell base parsing confusion

`$((39%2))`

: modulo operation: result is 0 (even week number) or 1 (odd week number), this week result is 1, next week 0

`test 1 -eq 1`

: arithmetic test (equal), in this case result is boolean true

`&& yourCommand`

: Boolean AND: run `yourCommand`

only if result of previous command was boolean true

Note that the year can get two odd weeks: 53 (this year) and 1 (next year)