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I once tried to fix one of the flaws of Vigenère and I came up with a slight modification but still keeping most of the simplicity.

https://blog.hackensplat.com/2011/02/vinegar.html

I then noticed that my new crypto-system itself has a flaw. Oh well.

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My 'gut' intuition is that doing that is the same as applying the cipher of length 2, then the cipher of length 3, 5, 7 each in turn invidually, but I haven't had the chance to dig out cyberchef to confirm this.

Edit: Indeed: (no spoilers for the fun of actually breaking your message)

https://gchq.github.io/CyberChef/#recipe=Vigen%C3%A8re_Encod...

Yes, my cipher is exactly the same as four rounds of Vigenère with 2,3,5,7 length keys, with the proviso that you can't go beyond 210 when all four keys meet again.

(I may go back and edit the text to make this clear.)

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