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 A285309 #22 Nov 23 2017 20:21:14
%S A285309 0,2,3,2,5,11,7,10,3,17,11,23,13,23,23,10,17,29,19,37,31,35,23,55,5,
%T A285309 41,30,51,29,71,31,42,47,53,47,41,37,59,55,85,41,95,43,79,68,71,47,
%U A285309 103,7,67,71,93,53,110,71,115,79,89,59,163,61,95,94,42,83,143,67,121,95,143,71,145,73,113,98
%N A285309 Sum of nonsquare divisors of n.
%H A285309 Antti Karttunen, <a href="/A285309/b285309.txt">Table of n, a(n) for n = 1..16384</a>
%H A285309 <a href="/index/Su#sums_of_divisors">Index entries for sequences related to sums of divisors</a>
%F A285309 G.f.: Sum_{k>=1} A000037(k)*x^A000037(k)/(1 - x^A000037(k)).
%F A285309 a(n) = A000203(n) - A035316(n).
%F A285309 a(A005117(n)) = A000203(A005117(n)) - 1.
%F A285309 a(p^(2*k-1)) = a(p^(2*k)) = p*(p^(2*k) - 1)/(p^2 - 1) for p is a prime and k >= 1.
%e A285309 a(6) = 11 because 6 has 4 divisors {1, 2, 3, 6} among which 3 are nonsquares {2, 3, 6} therefore 2 + 3 + 6 = 11.
%t A285309 Table[DivisorSum[n, # &, Mod[DivisorSigma[0, #], 2] == 0 &], {n, 1, 75}]
%t A285309 nmax = 75; Rest[CoefficientList[Series[Sum[(k + Floor[1/2 + Sqrt[k]]) x^(k + Floor[1/2 + Sqrt[k]])/(1 - x^(k + Floor[1/2 + Sqrt[k]])), {k, 1, nmax}], {x, 0, nmax}], x]]
%t A285309 Array[DivisorSum[#, # &, ! IntegerQ@ Sqrt@ # &] &, 75] (* _Michael De Vlieger_, Nov 23 2017 *)
%o A285309 (PARI) a(n) = sumdiv(n, d, if (!issquare(d), d)); \\ _Michel Marcus_, Apr 17 2017
%o A285309 (Python)
%o A285309 import gmpy
%o A285309 from sympy import divisors
%o A285309 def a(n): return sum([d for d in divisors(n) if gmpy.is_square(d)==0]) # _Indranil Ghosh_, Apr 18 2017
%Y A285309 Cf. A000037, A000203, A005117, A035316, A056595, A087153.
%K A285309 nonn
%O A285309 1,2
%A A285309 _Ilya Gutkovskiy_, Apr 16 2017