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 A103804 #10 Dec 18 2012 15:04:33
%S A103804 13,19,29,31,41,59,79,89,101,109,131,179,211,239,241,271,311,331,349,
%T A103804 409,421,449,499,509,521,541,601,619,701,751,821,839,881,1009,1091,
%U A103804 1181,1201,1319,1321,1399,1429,1459,1489,1531,1571,1619,1801,1949,1951
%N A103804 Primes p such that both 2p +/- 21 are primes.
%F A103804 p, 2p-21 and 2p+21 all are positive primes.
%t A103804 Select[Range[2000], PrimeQ[ # ] && PrimeQ[2# + 21] && PrimeQ[2# - 21] &]
%t A103804 Select[Prime[Range[4,500]],And@@PrimeQ[2#+{21,-21}]&] (* _Harvey P. Dale_, Dec 18 2012 *)
%Y A103804 Cf. A103802, A103803.
%K A103804 nonn
%O A103804 1,1
%A A103804 _Zak Seidov_, Feb 16 2005