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 A126240 #5 Feb 16 2014 18:29:40
%S A126240 11,29,31,41,71,211,251,349,439,461,751,1031,1051,1289,1291,1609,1667,
%T A126240 1723,2113,2417,2423,2503,2579,2711,2903,3079,3919,3967,4153,4271,
%U A126240 4591,4759,4951,5051,5399,5693,6173,6361,6451,6691,6733,7229,7541,7559,7793
%N A126240 Primes p such that p = prime(n+3)=(prime(n+6)+prime(n))/2.
%H A126240 Harvey P. Dale, <a href="/A126240/b126240.txt">Table of n, a(n) for n = 1..1000</a>
%t A126240 Do[If[(Prime[n + 6] + Prime[n])/2 == Prime[n + 3], Print[Prime[n + 3]]], {n, 1, 3000}]
%t A126240 Transpose[Select[Partition[Prime[Range[4000]],7,1],(First[#]+Last[#])/2==#[[4]]&]][[4]] (* _Harvey P. Dale_, Feb 16 2014 *)
%Y A126240 Cf. A006562, A119381, A126238-A126243.
%K A126240 nonn
%O A126240 1,1
%A A126240 _Artur Jasinski_, Dec 21 2006
%E A126240 Extended by _Ray Chandler_, Dec 27 2006