I am looking for a category of natural numbers (about <1000 is enough) with its properties.
Here's some examples :
2 - It is the first prime number.
1729 - It is the smallest number expressible as the sum of two cubes in two different ways.
Here's some bad examples that I don't focus on :
36 - It is the number that its half is equal to multiplying each digits (3 and 6 in this case).
69 - It is the number which has a sexual meaning.
36 is the bad example because it depends on the base 10.
Is there any site about this?
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$\begingroup$Wikipedia article List of numbers links to articles about individual numbers. They have covered all natural numbers up to 1000, and some beyond that range.
I like the subheading of the article:
$\endgroup$ $\begingroup$This is an incomplete list which may never be able to satisfy particular standards for completeness. You can help by expanding it ...
I don't think "category" is quite what you mean, maybe "catalogue"? Anyway as a printed reference there's David Wells' Dictionary of Curious and Interesting Numbers and online, there are wiki entries for small integers, e.g. 37
$\endgroup$ $\begingroup$(for example). Please see thread
$\endgroup$ $\begingroup$A site that has some curiosities about natural numbers are but as any site that lists curiosities it will be incomplete but perhaps it satisfies your needs.
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