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 A235989 #22 Jan 28 2014 19:19:08
%S A235989 1,2,6,10,12,28,76,120,312,588,672,888,1060,1264,1656,14496,17900,
%T A235989 22896,44676,71712,77688,95040,183600,233088,327424,411264,425376,
%U A235989 446016,453258,655776,1041120,1253304,2708640,5241856,5468352,8676576,9738912,12536640,59489184
%N A235989 sigma(n) is an additive inverse of n modulo phi(n).
%C A235989 sigma(10) = 18 is congruent to 2 = -10 mod 4 and phi(10) = 4; so 10 is a term of the sequence.
%C A235989 If p = 5*2^k-1 is a prime, as it happens for k = 2, 4, 8, 10, 12, 14,... (A001770), then n = 2^k*p is in the sequence, since n+sigma(n) = 6*phi(n). - _Giovanni Resta_, Jan 27 2014
%H A235989 Giovanni Resta, <a href="/A235989/b235989.txt">Table of n, a(n) for n = 1..59</a> (terms < 10^11)
%t A235989 t = {1}; For[i = 1, i <= 10^6, i++; If[Mod[DivisorSigma[1, i] + i, EulerPhi[i]] == 0, AppendTo[t, i]]]; t
%o A235989 (PARI) isok(n) = !((sigma(n) + n) % eulerphi(n)); \\ _Michel Marcus_, Jan 27 2014
%Y A235989 Cf. A001770.
%K A235989 nonn
%O A235989 1,2
%A A235989 _Joseph L. Pe_, Jan 27 2014
%E A235989 More terms from _Michel Marcus_, Jan 27 2014