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Mar 5, 2019 at 16:10 comment added user21820 I think you've misunderstood me from the very beginning. I'm not at all interested in formulating novel interesting conjectures. Neither do I care whether my random conjectures have been investigated before. What I asked clearly was whether there is any reason to believe that there are deep uniform reasons for such conjectures that have no small counter-examples. That's all.
Mar 5, 2019 at 16:00 comment added Zhi-Wei Sun I don't agree your viewpoint. What I mean is that it is not easy to formulate a really novel and interesting conjecture about primes that has not been investigated before.
Mar 5, 2019 at 13:54 comment added user21820 Thanks. Anyway I have no idea why you keep saying it's not new. I don't care whether it's new; it was just an example to show how easy it is to come up with conjectures of that kind where minor tweaks have relatively large counter-examples, and as I said in my first comment my question has always been about the small cases, not about the asymptotic behaviour. (And I upvoted your answer so I can't upvote it again...)
Mar 5, 2019 at 12:36 history edited Zhi-Wei Sun CC BY-SA 4.0
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Mar 5, 2019 at 12:33 comment added Zhi-Wei Sun See oeis.org/A065377 for the list of primes not of the form $p+k^2$ with $k>0$. Robert G. Wilson v wrote on Nov 05 2001 that "Probably finite and 7549 is the last entry." So I do consider your PSQ not new at all
Mar 5, 2019 at 12:30 history edited Zhi-Wei Sun CC BY-SA 4.0
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Mar 5, 2019 at 11:59 comment added user21820 Yes, but I was just saying that I cannot use the OEIS-cited search to claim that there are no counter-examples to my conjecture up to 3 billion. Asymptotically, I'd expect the number of decompositions to tend to infinity, as you say.
Mar 5, 2019 at 11:38 comment added Zhi-Wei Sun Actually, Hardy and Littlewood had a conjecture on the main term of the number $r(n)$ of ways to write a large non-square integer $n$ as the sum of a prime and a sqaure. According to their conjecture, $r(n)\to\infty$. This, of course, implies that large prime can be written as the sum of a prime and a positive square.
Mar 5, 2019 at 7:05 comment added user21820 Oh thanks yea I didn't see that. My results match theirs for non-primes, but I require a positive square so unfortunately their search doesn't cover primes.
Mar 5, 2019 at 6:57 comment added Zhi-Wei Sun It seems that you have not yet visited oeis.org/A020495 which lists all the known 21 terms which are neither squares nor primes plus squares. In the Extension part, it wrotes that "Almost certainly finite; no other terms below 25000000. Search extended to 3000000000 by James Van Buskirk without finding any more terms". - John Robertson (Jpr2718(AT)aol.com) (2009)
Mar 5, 2019 at 6:41 comment added user21820 Thanks, but as with Timothy's cited conjecture, this concerns asymptotic behaviour, whereas I'm asking about the small cases, i.e. below the bound where the asymptotic behaviour takes over.
Mar 5, 2019 at 3:22 history edited Zhi-Wei Sun CC BY-SA 4.0
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Mar 5, 2019 at 3:05 history edited Zhi-Wei Sun CC BY-SA 4.0
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Mar 5, 2019 at 2:59 history answered Zhi-Wei Sun CC BY-SA 4.0