Is that sequence on the OEIS yet?..
Thanks for the nerdsnipe, I definitely wanted to spend my Sunday looking at het sex in yuri works. Anyway, at first we have to establish that there's no actual Het on page 133, it's on page 24 (the numbering just goes across chapters).
That leaves us with 4,5,6,15,17,21,24,25,26, which ... isn't in the OEIS itself, but if we drop the single digits, it's a match for A191931. But wait, there's more! There also exist the tags Het on pages 17 and 19 and Het on pages 19 and 20. If we add the missing numbers (19 and 20) to our sequence, and again invoke the law of small siblings numbers (i.e. they're all shitheads) we get a match for A084463!
"But what about het rape?" I hear you ask. Do that yourself, I say.
But seriously, if I were a programming guy, I'd extend the tagging system to be able to tag individual pages, and aggregate over them automatically in the chapter page...
Yeah that would make more sense.
Besides the DB being probably not architecture for that use case, it's also simply not feasible with the current tag system. Not just the manual review (I have suggestions pending from early July) but also the way people use it to search and filter works: most tags really only make sense as a greater theme (think about all the School life manga that feature Sports at some point.) Also see the relevant FAQ entry.