The idiom some odd appears in two main uses: (1) following a number and meaning approximately or a little more than (e.g., “there were 50-some-odd people at the banquet”); and (2) in the phrase some odd reason, which means an unknown reason. In both uses, some odd is casual and might be considered out of place in formal contexts. The first one, especially, should be avoided when you need to sound authoritative, as it may signal that you haven’t done enough research to provide an exact figure.
In its numerical use, some odd implies that the exact number is not important. When it functions along with a number as a phrasal adjective preceding a noun, the whole phrase is hyphenated—for example:
The previously announced list of 30-some-odd bands doesn’t come with too many surprises. [Dallas Observer]
Especially when it’s 30-some-odd and raining, as well as blowing at 40 mph. [quoted in Pittsburgh Morning Sun]
And when a writer describes something as happening “for some odd reason,” it means the causes of the event are mysterious (at least to the writer)—for example:
For some odd reason, Peggy has to urinate in a cup. [OC Register]