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 A147820 #5 Nov 21 2013 12:49:27
%S A147820 1,2,3,4,5,6,7,8,9,10,11,12,14,15,16,18,19,20,21,22,23,24,26,27,29,30,
%T A147820 31,33,34,35,36,37,39,40,41,42,44,45,48,49,50,51,52,53,54,55,56,57,63,
%U A147820 64,65,66,68,69,70,74,75,76,78,79,81
%N A147820 Nearest-neighbors of odd primes, divided by 2.
%F A147820 a(n) = A147819(n)/2.
%t A147820 Union[Flatten[{(#-1)/2,(#+1)/2}&/@Prime[Range[2,40]]]] (* _Harvey P. Dale_, Oct 19 2011 *)
%Y A147820 Cf. A134926, A134933, A147819.
%K A147820 easy,nonn
%O A147820 1,2
%A A147820 _Omar E. Pol_, Nov 14 2008