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 A165681 #11 Feb 23 2017 02:46:39 %S A165681 13,17,19,23,37,41,47,61,71,73,79,83,97,101,103,107,113,127,131,139, %T A165681 149,151,163,167,179,181,191,193,199,211,223,227,229,233,241,251,257, %U A165681 263,269,271,277,281,283,293,307,311,317,331,337,349,359,367,373,379,383,397,401 %N A165681 Primes p such that 3*p*(p-1)+1 is not prime. %H A165681 Vincenzo Librandi, <a href="/A165681/b165681.txt">Table of n, a(n) for n = 1..1000</a> %F A165681 A000040 \ A165682. %F A165681 a(n) ~ n log n. - _Charles R Greathouse IV_, Feb 23 2017 %t A165681 Select[Prime[Range[90]],!PrimeQ[3#(#-1)+1]&] (* _Harvey P. Dale_, Mar 18 2011 *) %o A165681 (PARI) is(n)=isprime(n) && !isprime(3*n*(n-1)+1) \\ _Charles R Greathouse IV_, Feb 23 2017 %Y A165681 Cf. A165682, A165683. %K A165681 nonn,easy %O A165681 1,1 %A A165681 _Vincenzo Librandi_, Sep 24 2009 %E A165681 2 and 3 removed by _R. J. Mathar_, Sep 26 2009