For whatever it's worth, this problem seems to have its roots in Proto-Indo European, with only a few languages managing to shorten it from the original two-syllable word to one, although even in those cases it looks to me like the words still end up with two moras even if they do manage to fit in a single syllable.
Why not "sen"? If not for written language, seven would likely already be pronounced this way. The process was under way. Weeks were once called sennights. And even people who don't usually say it this way often do when drunk. True, there tends to be a glottal stop after the e before the n when the v is elided, but not always.
What to do about zero? Just reduce it to oh, like in casual speech or when reciting telephone numbers.
oh, one, two, three, four, five, six, sen, eight, nine, ten.
There! All single syllables.
Sincere response: Could work, but I weep for the lost clarity caused by sen and ten rhyming. Our current digits are beautifully unambiguous this way, whereas our alphabet is a horrible lost cause which had to be completely replaced over low-fidelity audio channels.
Sarcastic response: I'll agree iff 10 becomes teven.
Yeah that seems right to me too … I asked Claude for analogous cases and it brought up the historical dropping of sounds in the middle of the words “Wednesday”, “half”, and “chalk”.
That's the wise thing to do, but people routinely use oh. Five-oh-six-three-four-oh-one. In fact, zero might sound overly formal to me depending on the context. If I am reading my credit card number, I would say zero.
I do sort of the same thing, except I'm pretty sure I'm pronouncing the "e" in "sen" as a long "e" in the literal linguistic vowel-length sense. I wonder if this is how English gets phonemic vowel length back?
I do this (with "sev") when counting to myself. Nice to see the other people chose the same shelling point!
I don't like the number seven. Well, really the name of the number seven. All the other single digit numbers are single syllable, and seven has to go and take two. Seventy and seventeen have the same problem. What can we do?
I think the two main candidates are "sev" (dropping the second syllable) and "sen" (dropping the first coda and second onset). While I find "sen" slightly nicer on the tongue, I think "sev" is more promising because it feels like a better short form.
It feels like we ought to be able to switch to calling it "sev", where some people just start saying that and other people understand them? I've been playing around it, but every time I do my toddler Nora laughs at me as if I'm being ridiculously over the top: "you said sev!!" Does not bode well for a low-key migration.