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 A269256 #13 Sep 06 2017 11:30:16 %S A269256 7,11,17,19,23,29,31,41,47,53,59,67,71,83,89,101,107,113,127,131,137, %T A269256 139,149,167,179,181,191,197,199,211,227,233,239,251,257,263,269,281, %U A269256 293,307,311,317,347 %N A269256 Chen primes p such that there are Chen primes p > q > r in arithmetic progression. %C A269256 Green & Tao prove that this sequence is infinite. %H A269256 Charles R Greathouse IV, <a href="/A269256/b269256.txt">Table of n, a(n) for n = 1..10000</a> %H A269256 Ben Green and Terence Tao, <a href="http://jtnb.cedram.org/item?id=JTNB_2006__18_1_147_0">Restriction theory of the Selberg sieve, with applications</a>, Journal de théorie des nombres de Bordeaux 18:1 (2006), pp. 147-182. %e A269256 19 is in the sequence since 3 < 11 < 19, 19 - 11 = 11 - 3, all three are prime, and 3+2, 11+2, and 19+2 are each either prime or semiprime. %o A269256 (PARI) issemi(n)=bigomega(n)==2 %o A269256 ischen(n)=isprime(n) && (isprime(n+2) || issemi(n+2)) %o A269256 is(n)=if(!ischen(n), return(0)); forprime(p=2,n-4, if((p+n)%4==2 && ischen(p) && ischen((p+n)/2), return(1))); 0 %Y A269256 Subsequence of A109611. This is the Chen prime analog of A216495. %Y A269256 Cf. A291525. %K A269256 nonn %O A269256 1,1 %A A269256 _Charles R Greathouse IV_, Jul 12 2016