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 A103688 #16 Sep 09 2014 20:49:30
%S A103688 0,0,0,4,0,6,0,0,9,0,0,12,0,0,15,0,0,18,0,0,21,0,0,0,0,0,0,0,0,30,0,0,
%T A103688 0,0,0,0,0,0,0,0,0,42,0,0,0,0,47,0,0,0,51,0,0,0,0,0,0,0,0,60,0,0,0,0,
%U A103688 0,0,0,0,69,0,0,72,0,0,75,0,0,0,0,0,0,0
%N A103688 a(n) = n if A103689(n)*n +/- 1 are twin primes; a(n) = 0 otherwise.
%e A103688 For n=5 2*5-1=9 is not prime, 2*5+1=11 is prime so a(5)=0.
%e A103688 For n=6 1*6-1=5 is prime, 1*6+1=7 is prime, 5 and 7 are twin primes so a(6)=6.
%t A103688 lktp[n_]:=Module[{k=1},While[NoneTrue[k*n+{1,-1},PrimeQ],k++];If[AllTrue[k*n+{1,-1},PrimeQ],n,0]]; Array[lktp,100] (* The program uses the functions NoneTrue and AllTrue from Mathematica version 10 *) (* _Harvey P. Dale_, Sep 09 2014 *)
%o A103688 (PARI)
%o A103688 a(n)=k=1;while(!isprime(k*n+1)&&!isprime(k*n-1),k++);k
%o A103688 for(n=1,100,if(isprime(a(n)*n+1)&&isprime(a(n)*n-1),print1(n,", "));print1(0,", ")) \\ _Derek Orr_, Sep 09 2014
%Y A103688 Cf. A103689.
%K A103688 easy,nonn
%O A103688 1,4
%A A103688 _Pierre CAMI_, Feb 12 2005
%E A103688 Corrected by _Harvey P. Dale_, Sep 09 2014
%E A103688 Definition simplified by _Derek Orr_, Sep 09 2014