Talk:Highly composite number

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"The term was coined by Ramanujan (1915), who showed that there are infinitely many such numbers"[edit]

Isn't it a trivial consequence from the fact that there are numbers with arbitrarily large number of divisors? 132.65.251.182 (talk) 08:18, 23 June 2015 (UTC)

Yes, we shouldn't say a mathematician "showed" a completely trivial observation anyone could make. I have removed it.[1] PrimeHunter (talk) 23:12, 23 June 2015 (UTC)

For the half-asleep (including me when I first read that): there exists a number with k divisors, for any nonnegative integer k. (Example: 2^{k − 1} will have k divisors.) And since there are such numbers for each k, there must be a smallest one among them for each k. So we can construct a sequence, where the kth term is the smallest number that has k divisors. Then we can simply discard every term which is larger than a subsequent term. Voilà, the list of highly composite numbers.

Now how do we know that they don't run out, and that you don't discard nearly all terms? Simple. Suppose the last term in the HCN sequence is n. Then find an odd prime p that doesn't divide n (which is obviously always possible). pn > n (obviously). Now pn has all the factors of n, and then some (p of course, and the products of p and the factors of n). So it has more factors, so n cannot be the last term. Double sharp (talk) 09:53, 18 September 2015 (UTC)

Right. kn for any k > 1 would work, since kn is a divisor of itself but never of n. PrimeHunter (talk) 10:14, 18 September 2015 (UTC)

You're right, it's even simpler (I must've been mentally considering only proper divisors). The point stands, though. (^_^) Double sharp (talk) 13:01, 18 September 2015 (UTC)

What are the * for in the table?[edit]

The asterisk behind 2,4,5,9,10, ... doesn't seem to be explained anywhere. Maxiantor (talk) 14:47, 28 July 2016 (UTC)

They link to Superior highly composite number but it's probably too subtle. PrimeHunter (talk) 19:53, 28 July 2016 (UTC)

Table Doesn't Show the Divisors![edit]

The article is about a number "with more divisors than any smaller positive integer". And there's a big table of "the initial or smallest 38 highly composite numbers". But the table doesn't tells us what the divisors are!

For example, the 5th row of the table is for the number 12. And 4 is certainly a divisor of 12. But the number "4" doesn't appear anywhere in that row of the table. Seems to me that rather than listing the prime factors of numbers, or anyhow as well as, we should list the divisors. --johantheghost (talk) 08:16, 16 February 2020 (UTC)

@Johantheghost: The largest number in the table is 720720 with 240 divisors. That seems too much to list but I have added a table with divisors of the first 15 highly composite numbers.[2] If we added it as a new column in the existing table then the cells would become up to 32 lines high on narrow screens. PrimeHunter (talk) 23:21, 16 February 2020 (UTC)

@PrimeHunter: OK, thanks! Yeah, 240 is rather a lot... :-/ But this makes sense to me, we can at least see what divisors look like now (for folks who might be wondering). --johantheghost (talk) 16:46, 22 February 2020 (UTC)

Anh Duc Wiki -3

Tuesday, December 8, 2020