Why are the interest pages ordered this way?

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I see yoga is for example 13_210 (search yoga on mylot and check out the link name on top, it hasn't been discussed here at all ), scrapbooking is the first one with 13_22,but what happened to 13_1,13_2,13_3? It seems that they have no order or there is a much deeper mathematical sequence here that I must discover. Fellow mathematician let's work this out