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 A124049 #7 Dec 21 2014 12:21:17
%S A124049 0,3,9,81,123,57,87,243,69,63,189,231,1569,381,231,1443,1113,321,339,
%T A124049 1353,363,519,1323,1503,741,1221,957,1053,339,5931,2121,2301,2031,
%U A124049 4773,4737,10281,1317,129,3873,1443,387,11769,8271,5337,2883,7137,8193,8493
%N A124049 a(n) = c is least number such that 10^n/2 -/+ c are primes.
%C A124049 Related to Goldbach pairs of 10^n: a(n)=10^n/2 -A124450(n) Lesser of pair of closest primes whose sum is 10^n. Cf. A124013 Lesser of pair of most widely separated primes whose sum is 10^n, A065577 Number of Goldbach partitions of 10^n
%C A124049 All terms are divisible by 3 - see A108163.
%e A124049 Next terms up to n = 101: 14637, 9897,
%e A124049 6471, 183, 8043, 6921,6699, 29127, 3663, 12537, 3777,
%e A124049 6741, 2253, 561, 3783, 26979, 16491, 6543, 10683,
%e A124049 1749, 6417, 38871, 22767, 62403, 8631, 4497, 20739,
%e A124049 453, 16731, 25293, 4341, 37467,
%e A124049 55323,4587,37083,24717,6687,8763,22551,29367,37881,14301,8637,34101,22179,26811,7059,1647
%t A124049 lnc[n_]:=Module[{c=0,t=10^n/2},While[!AllTrue[t+{c,-c},PrimeQ],c++];c]; Array[ lnc,50] (* The program uses the AllTrue function from Mathematica version 10 *) (* _Harvey P. Dale_, Dec 21 2014 *)
%Y A124049 Cf. A065577, A124013, A124450.
%K A124049 nonn
%O A124049 1,2
%A A124049 _Hans Havermann_ and _Zak Seidov_, Nov 03 2006