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 A172458 #10 Aug 27 2024 18:39:57
%S A172458 1,4,8,10,12,14,16,18,20,22,24,26,27,33,34,35,39,40,42,44,45,48,49,50,
%T A172458 52,55,56,57,63,64,65,66,68,70,74,76,78,81,82,84,86,87,91,95,98,100,
%U A172458 105,106,111,112,115,116,117,119,121,125,126,128,129,132,134,136,138,140
%N A172458 Nonprimes n such that exactly one of 2n-1 and 2n+1 is prime.
%H A172458 Harvey P. Dale, <a href="/A172458/b172458.txt">Table of n, a(n) for n = 1..1000</a>
%t A172458 Select[Range[150],!PrimeQ[#]&&Total[Boole[PrimeQ[2 #+{1,-1}]]]==1&] (* _Harvey P. Dale_, Aug 27 2024 *)
%K A172458 nonn,easy,less
%O A172458 1,2
%A A172458 _Juri-Stepan Gerasimov_, Feb 03 2010
%E A172458 Edited by _Charles R Greathouse IV_, Mar 25 2010