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 A283105 #14 Jul 24 2017 20:02:17
%S A283105 4,9,12,25,45,49,121,169,289,361,529,637,841,961,1369,1681,1849,2209,
%T A283105 2809,3481,3721,4489,5041,5329,6241,6889,7921,9409,10201,10609,11449,
%U A283105 11881,12769,13357,16129,17161,18769,19321,22201,22801,24649,26569,27889,29929,32041,32761,36481,37249,38809,39601,44521
%N A283105 Numbers that are an integer multiple of the mean of their smallest and largest nontrivial divisors.
%C A283105 No prime is in the sequence since there are no nontrivial divisors of a prime.
%C A283105 The sequence includes every number that is the square of a prime.
%C A283105 It is easy to show that the other terms are of the form (2p-1)*p^2 where p and 2p-1 are prime. Therefore, the mean of the two divisors in question is always an integer.
%H A283105 Harvey P. Dale, <a href="/A283105/b283105.txt">Table of n, a(n) for n = 1..600</a>
%e A283105 4 is in the sequence because its smallest nontrivial divisor is 2, its largest nontrivial divisor is 2, and their mean is 2.
%e A283105 45 is in the sequence because its smallest nontrivial divisor is 3, its largest nontrivial divisor is 15, and their mean is 9, a divisor of 45.
%e A283105 10 is not in the sequence because it is not an integral multiple of 7/2, the mean of 2 and 5.
%t A283105 mslndQ[n_]:=Module[{d=Divisors[n]},Divisible[n,Mean[{d[[2]],d[[-2]]}]]]; Select[Range[2,50000],mslndQ] (* _Harvey P. Dale_, Jul 24 2017 *)
%o A283105 (PARI) is(n) = my(d=divisors(n), m=(d[2]+d[#d-1])/2); if(n%m==0, 1, 0) \\ _Felix Fröhlich_, Feb 28 2017
%Y A283105 Cf. A005382, A088595.
%K A283105 nonn
%O A283105 1,1
%A A283105 _Emmanuel Vantieghem_, Feb 28 2017