"An interrogative + か" means "some~".
e.g.
いつ(when) --> いつか(someday/sometime)
どこ(where) --> どこか(somewhere)
誰(who) --> 誰か(someone)
何(what) --> 何か(something)
As for the first example, it's also possible to interpret that か shows the preceding clause is an embeded question "Tell me what the number (of it) is.".