[seqfan] Re: Help me understand these sequences

Klaus Brockhaus klaus-brockhaus at t-online.de
Mon Mar 29 16:09:12 CEST 2010

Is it worth your (and our) time and efforts if the author doesn't respond?

       Klaus Brockhaus

Charles Greathouse schrieb:
> A171994 ("Twin natural nonprimes are products of free primes."):
> I can see that the members all have three prime factors, but I don't
> know what makes them twin natural nonprimes.  The definitions
> elsewhere suggest that this means numbers n with n+2 nonprime, but
> then why are 8 and 63 not in the sequence?  (And others beside: I
> don't think it's a case of an omission but my misunderstanding,)  And
> the numbers don't have n+2 with 3 prime factors either, so that theory
> also fails.  [I sent a similar message to the sequence author with no
> response.]
> A144565 ("a(n)=p-th digit of 2^(1/2) where p = n-th prime."):
> By the description, this is a duplicate of A090204.  But the values
> don't match at all.  What is this?
> Charles Greathouse
> Analyst/Programmer
> Case Western Reserve University

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