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 A104279 #14 Sep 08 2022 08:45:17 %S A104279 1,5,8,11,14,18,20,23,26,29,33,35,39,41,44,48,50,53,56,63,65,68,74,78, %T A104279 81,83,86,89,95,98,105,111,113,116,119,125,128,131,134,138,140,146, %U A104279 153,155,158,165,168,173,176,179,183,186,189,191,194,198,200,204,209,215 %N A104279 Numbers n such that 2n+1 is prime and 2n-1 is not prime. %H A104279 Robert Israel, <a href="/A104279/b104279.txt">Table of n, a(n) for n = 1..10000</a> %e A104279 a(1)=1 because 3 is prime and 1 is not prime. %e A104279 a(2)=5 because 11 is prime and 9 is not prime. %p A104279 filter:= n -> isprime(2*n+1) and not isprime(2*n-1): %p A104279 select(filter, [$1..300]); # _Robert Israel_, Apr 27 2020 %t A104279 Select[ Range[218], PrimeQ[2# + 1] && !PrimeQ[2# - 1] &] (* _Robert G. Wilson v_, Apr 18 2005 *) %o A104279 (Magma) [n: n in [1..220]| not IsPrime(2*n-1) and IsPrime(2*n+1)] // _Vincenzo Librandi_, Jan 28 2011 %o A104279 (PARI) is(n)=isprime(2*n+1) && !isprime(2*n-1) \\ _Charles R Greathouse IV_, Jun 13 2017 %Y A104279 Cf. A040040 and others. %K A104279 easy,nonn %O A104279 1,2 %A A104279 _Alexandre Wajnberg_, Apr 17 2005 %E A104279 More terms from _Robert G. Wilson v_, Apr 18 2005