This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A228374 #10 Sep 08 2022 08:46:05 %S A228374 1,2,5,6,7,8,10,11,12,13,14,17,18,19,20,22,23,24,25,26,27,28,29,30,31, %T A228374 32,33,34,35,36,38,39,41,42,43,44,45,46,48,49,50,52,53,54,57,58,59,60, %U A228374 61,62,63,64,65,66,67,68,69,70,72,73,75,76,77,78,79,80,81,82 %N A228374 Numbers n such that 2*prime(n) - prime(n+1) is not prime. %C A228374 Complement of A216075. %H A228374 Vincenzo Librandi, <a href="/A228374/b228374.txt">Table of n, a(n) for n = 1..1000</a> %e A228374 7 is in the sequence because 2*17-19=15 and 15 is not prime. %t A228374 f[n_]: = (2 Prime[n] - Prime[n + 1]); Select[Range[110], ! PrimeQ[f[#]]&] %t A228374 Flatten[Position[2#[[1]]-#[[2]]&/@Partition[Prime[Range[100]],2,1],_?(!PrimeQ[#]&)]] (* _Harvey P. Dale_, Jan 12 2016 *) %o A228374 (Magma) [n: n in [1..100]| not IsPrime(2*NthPrime(n) - NthPrime(n+1))]; %Y A228374 Cf. A216075. %K A228374 nonn,easy %O A228374 1,2 %A A228374 _Vincenzo Librandi_, Aug 21 2013