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 A076666 #13 Feb 11 2014 19:05:32 %S A076666 2012,2096,15892,17888,39916,102784,141008,146227,482144,487865, %T A076666 1321312,1887008,2749057,3513881,7141158,16767172,17503912,28122834, %U A076666 30534728,37453779,42140437,60994100,67777337,78251933,113091820,113768920,129868059,199240914,240859196,302897372 %N A076666 Numbers n such that sigma(n) + sigma(n+3) = sigma(n+1) + sigma(n+2). %C A076666 Each term of the sequence marks the start of four consecutive sigma-values for which the sum of the means equals the sum of the extremes. %H A076666 Giovanni Resta, <a href="/A076666/b076666.txt">Table of n, a(n) for n = 1..90</a> (terms < 4*10^12) %e A076666 sigma(2012) + sigma(2015) = 3528 + 2688 = 6216; sigma(2013) + sigma(2014) = 2976 + 3240 = 6216, so 2012 is a term of the sequence. %t A076666 Select[Range[10^5], DivisorSigma[1, # ] + DivisorSigma[1, # + 3] == DivisorSigma[1, # + 1] + DivisorSigma[1, # + 2] &] %Y A076666 Cf. A000203, A055574, A065900, A073500, A099632, A226361, A226475. %K A076666 nonn %O A076666 1,1 %A A076666 _Joseph L. Pe_, Oct 25 2002 %E A076666 a(6)-a(26) from _Donovan Johnson_, Feb 01 2009 %E A076666 a(27)-a(30) from _Alex Ratushnyak_, Jun 29 2013