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 A168011 #15 Oct 23 2023 11:37:12 %S A168011 5,20,45,84,131,198,273,368,473,602,731,894,1061,1252,1457,1686,1917, %T A168011 2186,2453,2752,3065,3402,3743,4122,4509,4918,5345,5804,6249,6754, %U A168011 7251,7780,8333,8906,9477,10104,10729,11386,12047,12758,13445,14202,14945 %N A168011 a(n) = Sum of all numbers of divisors of all numbers < (n+1)^2. %C A168011 Partial sums of A168010. %H A168011 Chai Wah Wu, <a href="/A168011/b168011.txt">Table of n, a(n) for n = 1..10000</a> %e A168011 a(2)=20 because the numbers < (2+1)^2 are 1,2,3,4,5,6,7 and 8. Then a(2) = d(1)+d(2)+d(3)+d(4)+d(5)+d(6)+d(7)+d(8) = 1+2+2+3+2+4+2+4 = 20, where d(n) is the number of divisor of n (see A000005). %t A168011 f[n_] := Plus @@ DivisorSigma[0, Range[(n + 1)^2 - 1]]; Array[f, 43] (* _Robert G. Wilson v_, Dec 10 2009 *) %o A168011 (Python) %o A168011 def A168011(n): %o A168011 m = n*(n+2) %o A168011 return (sum(m//k for k in range(1,n+1))<<1)-n**2 # _Chai Wah Wu_, Oct 23 2023 %Y A168011 Cf. A000005, A168010, A168012, A168013. %K A168011 nonn %O A168011 1,1 %A A168011 _Omar E. Pol_, Nov 16 2009 %E A168011 More terms from _Robert G. Wilson v_, Dec 10 2009