"One thousand nine hundred and forty five."
Translation:Seribu sembilan ratus empat puluh lima.
Why do you assume it makes sense to put the "and" in Indonesian? I mean, I don't know, maybe it does. But it wouldn't in my native Polish, for example. Just the fact that it's used in English (and I believe it's rather American English and not necessarily British) doesn't mean it's used in other languages.
Don't take it wrong. Like you, I also don't want the awkward "dan" there. I never assume it makes sense to put the "dan" in the context of that Indonesian expression. In fact, the "and" in that context is redundant and unnecessary in Chinese, Japanese and many languages as well, and I really don't want to add the "dan" there in my answer because I know it is implicit. However, in many Duolingo practice questions here, every word including the conjunction was required to be translated to show that you know the meaning of all the words; so when the question has the "and" then the answer has to have the corresponding "dan" or else it would be marked wrong for missing the translation of the "and". Similarly, according to Duolingo's usual marking practice, when the question does not contain the word "and", the answer is assumed not to have the "dan". Thus I could only assume that the matching "dan" is necessary here to get the answer correct. All I have said is that since the "and" is in this question, although it is implicit, any answer with or without the "dan" should be treated as correct even when in daily life we don't usually put the "dan" there.