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 A089681 #11 Jun 05 2017 10:13:48 %S A089681 1,2,4,6,8,12,14,18,22,26,28,30,34,40,44,48,50,52,54,58,60,70,72,74, %T A089681 76,78,92,96,110,118,122,136,138,144,150,154,158,164,176,182,186,188, %U A089681 204,210,214,216,230,232,234,236,242,248,260,268,272,274,280,298,304,308 %N A089681 Numbers n such that 3n^2 - 1 is prime. %D A089681 M. Cerasoli, F. Eugeni and M. Protasi, Elementi di Matematica Discreta, Bologna 1988 %D A089681 Emanuele Munarini and Norma Zagaglia Salvi, Matematica Discreta,UTET, CittaStudiEdizioni, Milano 1997 %H A089681 Harvey P. Dale, <a href="/A089681/b089681.txt">Table of n, a(n) for n = 1..1000</a> %t A089681 Select[Range[500],PrimeQ[3#^2-1]&] (* _Harvey P. Dale_, Oct 09 2011 *) %o A089681 (PARI) is(n)=isprime(3*n^2-1) \\ _Charles R Greathouse IV_, Jun 05 2017 %K A089681 easy,nonn %O A089681 1,2 %A A089681 _Giovanni Teofilatto_, Jan 05 2004 %E A089681 More terms from _Rick L. Shepherd_, May 18 2005