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The single or isolated numbers. The union of single (or isolated or non-twin) primes and single (or isolated or average of twin prime pairs) nonprimes.
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%I #17 May 17 2024 03:27:53

%S 2,4,6,12,18,23,30,37,42,47,53,60,67,72,79,83,89,97,102,108,113,127,

%T 131,138,150,157,163,167,173,180,192,198,211,223,228,233,240,251,257,

%U 263,270,277,282,293,307,312,317,331,337,348,353,359,367,373,379,383,389

%N The single or isolated numbers. The union of single (or isolated or non-twin) primes and single (or isolated or average of twin prime pairs) nonprimes.

%C Equals A007510 U A014574.

%H Charles R Greathouse IV, <a href="/A167706/b167706.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) ~ n log n. - _Charles R Greathouse IV_, Apr 29 2015

%t With[{nn = 78}, {2}~Join~Union[Transpose[Select[Partition[Prime@ Range@ nn, 3, 1], And[#[[2]] - #[[1]] != 2, #[[3]] - #[[2]] != 2] &]][[2]], Map[Mean, Select[Partition[Prime@ Range@ nn, 2, 1], Differences@ # == {2} &]]]] (* _Michael De Vlieger_, Feb 22 2017, after _Harvey P. Dale_ at A007510 and A014574 *)

%o (PARI) is(n)=if(n%6, (isprime(n) && !isprime(n-2) && !isprime(n+2)) || n==4, isprime(n-1) && isprime(n+1)) \\ _Charles R Greathouse IV_, Apr 29 2015

%o (PARI) lista(pmax) = {my(p1 = 2, p2 = 3); print1(2, ", "); forprime(p3 = 5, pmax, if(p2 == p1 + 2, print1(p1 + 1, ", ")); if(p2 != p1 + 2 && p2 != p3 - 2, print1(p2, ", ")); p1 = p2; p2 = p3);} \\ _Amiram Eldar_, May 17 2024

%Y Cf. A007510, A014574.

%K nonn

%O 1,1

%A _Juri-Stepan Gerasimov_, Nov 10 2009, Nov 14 2009

%E Corrected (97 inserted) by _R. J. Mathar_, Nov 16 2009