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 A132748 #17 Dec 19 2018 22:17:17
%S A132748 0,3,0,3,0,6,0,3,0,3,0,10,0,3,0,3,0,6,0,12,0,3,0,10,0,3,0,3,0,17,0,3,
%T A132748 0,3,0,10,0,3,0,12,0,19,0,3,0,3,0,10,0,3,0,3,0,6,0,18,0,3,0,21,0,3,0,
%U A132748 3,0,6,0,3,0,3,0,27,0,3,0,3,0,6,0,12,0,3,0,23,0,3,0,3,0,36,0,3,0,3,0,10,0,3
%N A132748 a(n) = the sum of the positive non-isolated divisors of n.
%C A132748 A divisor, d, of n is non-isolated if either (d-1) or (d+1) divides n.
%C A132748 a(2n-1) = 0 for all n >= 1.
%H A132748 Antti Karttunen, <a href="/A132748/b132748.txt">Table of n, a(n) for n = 1..20000</a>
%F A132748 a(n) = A000203(n) - A132882(n), where A000203 is sigma(n), sum of divisors of n.
%e A132748 The positive divisors of 20 are 1,2,4,5,10,20. Of these, 1 and 2 are next to each other and 4 and 5 are next to each other. So a(20) = 1+2+4+5 = 12.
%t A132748 Table[Plus @@ (Select[Divisors[n], If[ # > 1,Mod[n, #*(# - 1)] == 0] || Mod[n, #*(# + 1)] == 0 &]), {n, 1, 80}] (* _Stefan Steinerberger_, Nov 01 2007 *)
%o A132748 (PARI) A132748(n) = sumdiv(n,d,((!(n%(1+d)))||((d>1)&&(!(n%(d-1)))))*d); \\ _Antti Karttunen_, Dec 19 2018
%Y A132748 Cf. A129308, A132747, A133565.
%K A132748 nonn
%O A132748 1,2
%A A132748 _Leroy Quet_, Aug 27 2007
%E A132748 More terms from _Stefan Steinerberger_, Nov 01 2007
%E A132748 Extended by _Ray Chandler_, Jun 24 2008