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 A131021 #12 Nov 01 2012 17:52:50
%S A131021 13,101,739,751,1301,1459,1471,1483,1583,1619,1877,1889,1949,2213,
%T A131021 2239,2351,2381,2441,2473,2549,2741,2917,3271,3413,3863,4133,4567,
%U A131021 4987,5081,5279,5347,5783,5813,6719,7027,7369,7459,7607,8233,8291,9151,9187,9397
%N A131021 Prime semiperimeters of quadrilaterals with sides which are four consecutive primes.
%C A131021 These are the prime numbers in A131019(k), occurring at k=1, 13, 71, 72, 116, 127, 128, 129, 136, 138, 157, 158, 162, 183, 185, ....
%H A131021 Zak Seidov, <a href="/A131021/b131021.txt">Table of n, a(n) for n = 1..1000</a>
%F A131021 A131019 INTERSECT A000040.
%p A131021 for n from 1 to 1000 do a131019 := add(ithprime(n+i),i=1..4)/2 : if isprime(a131019) then printf("%d, ",a131019) ; fi ; od:
%t A131021 Select[(Total /@ Partition[Prime[Range[10^3]], 4, 1])/2, PrimeQ] (* _Zak Seidov_, Nov 01 2012 *)
%o A131021 (PARI) p=3;q=5;r=7;forprime(s=11,1e4,if(isprime(t=(p+q+r+s)/2),print1(t", ")); p=q; q=r; r=s) \\ _Charles R Greathouse IV_, Nov 01 2012
%K A131021 easy,nonn
%O A131021 1,1
%A A131021 _R. J. Mathar_ and _Jonathan Vos Post_, Jun 12 2007