This sort of numbering system is quite common in UK schools, where the complex problems of time-tabling in a large school is often solved by the introduction of a two-week cycle. Rather than have - say -14 weeks in a term, numbered 1-14, they just have two numbers. They are not called 'odd' or 'even'; they are called 'week 1' and 'week 2'.
20/30 years ago, when my choir rehearsed in various schools, it initially seemed strange to me (a child of the '60s, when all schools had a weekly time-table) to see notices in schools saying 'This is week1/2'; but now it seems quite normal. A similar approach is taken in various other time-tabling contexts (for example, rubbish/recycling collections -
Week 1 and Week 2 Collection Dates ).
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