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 A099631 #13 Feb 01 2015 12:49:23
%S A099631 5,8,32,44,116,184,356,764,815,1004,1012,1205,1338,1345,1436,2636,
%T A099631 2876,3126,3644,5156,5305,5804,6236,7192,7542,7556,8564,9356,9404,
%U A099631 10196,10362,10904,11276,11876,13436,16375,17564,17636,20156,25316,25964
%N A099631 Numbers n such that (sigma(n-2)+sigma(n+2))/2 = sigma(n).
%H A099631 Harvey P. Dale, <a href="/A099631/b099631.txt">Table of n, a(n) for n = 1..1000</a>
%e A099631 n=5, {n-2,n+2}={3,7}, sigma(3)=4, sigma(7)=8, and sigma(5)=6=(4+8)/2.
%p A099631 with(numtheory); A099631:=n->`if`(sigma(n)=(sigma(n-2)+sigma(n+2))/2, n, NULL); # _Wesley Ivan Hurt_, Feb 03 2014
%t A099631 Flatten[Position[Partition[DivisorSigma[1,Range[30000]],5,1],_?((Last[ #]+ First[ #])/2==#[[3]]&),{1},Heads->False]]+2 (* _Harvey P. Dale_, Feb 01 2015 *)
%o A099631 (PARI) isok(n) = (sigma(n-2) + sigma(n+2))/2 == sigma(n); \\ _Michel Marcus_, Dec 30 2013
%Y A099631 Cf. A000203.
%K A099631 nonn
%O A099631 1,1
%A A099631 _Labos Elemer_, Oct 26 2004