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 A126242 #5 Jul 18 2013 14:33:58
%S A126242 41,61,71,89,181,373,397,433,449,863,907,911,937,941,983,1193,1259,
%T A126242 1931,2243,2251,2447,3359,3361,3823,3851,4057,4093,5231,5297,5417,
%U A126242 5813,6421,6619,7013,7151,7487,7583,7907,8171,8537,8563,8573,8581,9157,9257,9377
%N A126242 Prime numbers p such that p = prime(n+4)=(prime(n+8)+prime(n))/2.
%H A126242 Harvey P. Dale, <a href="/A126242/b126242.txt">Table of n, a(n) for n = 1..1000</a>
%t A126242 Do[If[(Prime[n + 8] + Prime[n])/2 == Prime[n + 4], Print[Prime[n + 4]]], {n, 1, 3000}]
%t A126242 Transpose[Select[Partition[Prime[Range[1200]],9,1],(First[#]+Last[#])/2 == #[[5]]&]][[5]] (* _Harvey P. Dale_, Jul 18 2013 *)
%Y A126242 Cf. A006562, A119381, A126238-A126243.
%K A126242 nonn
%O A126242 1,1
%A A126242 _Artur Jasinski_, Dec 21 2006
%E A126242 Extended by _Ray Chandler_, Dec 27 2006