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thanks for your interesting comment @stpro1 also Intel skipped core i4 and i6 too!

I think they only use odd numbers to name their processors. i3, i5, i7, and now i9 have odd numbers and no even numbers. Conspiracy theory?

NO Conspiracy theory - I think simply to avoid confusion with number of cores.

more info : https://www.quora.com/Why-did-Intel-name-their-processors-as-i3-i5-and-i7-instead-of-i2-i4-and-i6-or-i1-i2-i3-i4-and-so-on

Ah, that makes sense!