A closer approach to numbers

Hi, Maria. As mere curiosity but also because of the variety of answers I have got to these questions I really have many doubts about how numbers are written in Italian. First, I've found in some sources that in every number with the ending -tre, we must have an acute accent (e.g. veintitré, sessantatré). Is this true always? I have specific doubts with the number 103. As well, I' ve also seen that in some books the numbers are not separated, for example: tremilanovecientosessantasei (3.966), or seicentosessantamilasettecentosessantasei (660.766). I want to know if this is the way of writing numbers, or in any case, if it's possible to write them like this and if I can separate them. Finally, I would appreciate to have some examples of written numbers just to make myself sure as I think that being able to manage numbers accurately is extremely important in any language: *1.000.001 *1.001.003 *2.000.199 *850.500.073 *1.000.000.000 *1.001.000.000 I would much appreciate the help, just to be certain about how to deal with any possible quantity I encounter. Thank you very much and don't stop updating this course, it's fabulous and it has helped me a lot.