U1

[ SmokeDetector | MS ] Link at beginning of answer (34): Compound angle formulas by Naresh Patkare on math.SE

[ SmokeDetector | MS ] Link at beginning of answer (34): Proof of Compound Angle from Ptolemy's Theorem by Naresh Patkare on math.SE

[ SmokeDetector | MS ] Link at beginning of answer, blacklisted user (105): division in modular arithmetic by Naresh Patkare on math.SE

For closure:

3740589

For deletion:

3747194

3748024

3735350(closure)

C1 psq math.stackexchange.com/q/3751006/29335

A question of mine refers to U1? this deleted question. Therefore I decided to try and edit it into shape. It is unlikely that I want to add much more to it for then it would become my question. So I quite understand if you still think it is not good enough. I'm not suggesting that it should be opened. Only soliciting opinions about un/deletion.

@JyrkiLahtonen It may be worth noting that we know that there are not just infinitely many primes, but infinitely many non-twin primes. Most of the answers seem to assume that the question is about non-twin primes, rather than the stronger condition that both $p-2$ and $p+2$ are composite.

Otherwise, using my "If I can't imagine how extra context would improve the question" standard, I would be willing to vote to undelete / reopen.

But then this answer would need to be deleted.

I guess the question kind of asserts this non-twin prime thing, but there was clearly some confusion form teh answerers

@JyrkiLahtonen Actually, the question appears to be a duplicate. This seems to answer it.

@Xander I don't think they are duplicates. The one you found (I also visited it before posting here) is about infinitude of primes that are not the lower sibling of a twin pair. This question asks whether there are infinitely many primes that don't have a twin. It is easy to settle that with Brun's theorem, like one of the answerers did.

Do observe that one of the answers was deleted separately (for misunderstanding the question and answering the "duplicate" we found).

@JyrkiLahtonen I am confused about how the answer I linked doesn't answer teh question:

> Dolda2000 noted that a more interesting question is whether there are infinitely many primes that are not members of a twin pair. For this we can use the fact that there are infinitely many primes of the form 15𝑘±7. If 𝑝 is such a prime, then one of 𝑝−2 or 𝑝+2 is divisible by 3, and the other is divisible by 5, so if 𝑝>7 then neither 𝑝−2 nor 𝑝+2 is prime.

@XanderHenderson Sorry, I thought you referred to that question instead of the add-on in André Nicolas's answer. Should have read it more carefully. I haven't been careful lately :-(

Closing as a duplicate becomes then an option.

C1. A pretty blatant expectation that someone at math.se answer their question for them.