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 A185027 #43 Oct 17 2024 10:14:09
%S A185027 1,1,4,1,1,10,1,1,4,11,1,10,1,1,19,1,1,10,1,11,25,1,1,10,1,1,4,29,1,
%T A185027 35,1,1,4,1,1,46,1,1,4,11,1,31,1,1,64,1,1,10,1,11,4,1,1,10,56,29,4,1,
%U A185027 1,35,1,1,25,1,1,76,1,1,4,11,1,46,1,1,19,1,1,88,1
%N A185027 Sum of the triangular divisors of n.
%H A185027 Antonio Roldán, <a href="/A185027/b185027.txt">Table of n, a(n) for n = 1..10000</a>
%F A185027 G.f.: Sum_{k>=1} (k*(k + 1)/2)*x^(k*(k+1)/2)/(1 - x^(k*(k+1)/2)). - _Ilya Gutkovskiy_, Dec 24 2016
%e A185027 a(15) = 19 because 1+3+15 = 19 (1, 3 and 15 are the triangular divisors of 15).
%t A185027 a[n_] := DivisorSum[n, # &, IntegerQ[Sqrt[8*#+1]] &]; Array[a, 100] (* _Amiram Eldar_, Aug 12 2023 *)
%o A185027 (PARI)
%o A185027 istriang(x)=issquare(8*x+1)
%o A185027 a(n)={my(m=0);for(i=1,n,if(istriang(i)&&n/i==n\i,m+=i));return(m)}
%o A185027 {for(n=1,10^4,k=sumdivtriang(n);write("b185027.txt",n," ",k))}
%o A185027 (PARI) a(n)=sumdiv(n, d, ispolygonal(d, 3)*d) \\ _Charles R Greathouse IV_, Jan 14 2013
%Y A185027 Cf. A000217, A035316.
%K A185027 nonn,easy
%O A185027 1,3
%A A185027 _Antonio Roldán_, Jan 14 2013