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 A085831 #20 Oct 13 2021 19:15:00
%S A085831 1,3,8,20,50,119,280,645,1466,3280,7262,15937,34720,75108,161552,
%T A085831 345785,736974,1564762,3311206,6985780,14698342,30850276,64607782,
%U A085831 135030018,281689074,586636098,1219788256,2532608855,5251282902,10874696106,22493653324,46475828418
%N A085831 a(n) = Sum_{k=1..2^n} d(k) where d(n) = number of divisors of n (A000005).
%H A085831 Chai Wah Wu, <a href="/A085831/b085831.txt">Table of n, a(n) for n = 0..82</a> (terms 0..64 from Donovan Johnson)
%t A085831 k = s = 0; Do[ While[ k < 2^n, k++; s = s + DivisorSigma[ 0, k ]]; Print[s], {n, 0, 29} ]
%o A085831 (Python)
%o A085831 from math import isqrt
%o A085831 def A085831(n): return (lambda m, r: 2*sum(r//k for k in range(1, m+1))-m*m)(isqrt(2**n),2**n) # _Chai Wah Wu_, Oct 08 2021
%o A085831 (PARI) a(n) = sum(k=1, 2^n, numdiv(k)); \\ _Michel Marcus_, Oct 10 2021
%Y A085831 Cf. A006218, A050226, A085567, A085829, A057494.
%K A085831 nonn
%O A085831 0,2
%A A085831 _Robert G. Wilson v_, Sep 21 2000