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 A226949 #19 Dec 25 2019 04:51:04
%S A226949 0,1,1,2,0,4,1,0,2,2,0,4,0,1,4,2,1,6,1,3,2,2,1,5,2,1,3,1,2,11,0,1,4,2,
%T A226949 2,6,0,2,4,3,1,9,2,3,4,3,1,7,1,4,5,5,0,8,4,1,3,3,1,15,0,3,4,4,4,13,3,
%U A226949 4,4,5,3,10,0,3,11,2,3,12,0,6,6,3,2,13,3
%N A226949 Number of twin prime pairs of the form k*n +/- 1 with k <= n.
%H A226949 Amiram Eldar, <a href="/A226949/b226949.txt">Table of n, a(n) for n = 1..10000</a>
%e A226949 a(4) = 2 because there are two twin prime pairs of the form (4k - 1,4k + 1) with 1 <= k <= 4, namely (3, 5) for k = 1 and (11, 13) for k = 3.
%t A226949 a[n_] := Sum[Boole[PrimeQ[k*n - 1] && PrimeQ[k*n + 1]], {k, 1, n}]; Array[a, 100] (* _Amiram Eldar_, Dec 25 2019 *)
%o A226949 (PARI) a(n)=sum(k=1,n,isprime(k*n-1)&&isprime(k*n+1)) \\ _Charles R Greathouse IV_, Jun 27 2013
%Y A226949 Cf. A014574, A071558.
%K A226949 nonn
%O A226949 1,4
%A A226949 _Irina Gerasimova_, Jun 23 2013
%E A226949 a(7), a(20), a(36) corrected by _Charles R Greathouse IV_, Jun 27 2013
%E A226949 a(54)-a(90) from _Charles R Greathouse IV_, Jun 27 2013