Is there in Czech only one meaning of the word "number"? Because in Russian there are two words - "номер" (nomer, e.g. phone number, number of the room etc.) and "число" (chislo, e.g. the number "3", Fibonacci numbers etc.).
Fibonacci's number and phone number are both číslo in Czech. Though typically asking a girl for a 'number' without specifying you do not mean Fibonacci's would do. :D