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 A023858 #11 Jun 13 2019 20:49:28
%S A023858 0,1,2,0,1,2,3,4,6,2,3,4,5,7,9,11,13,5,6,8,10,12,14,16,18,20,23,11,13,
%T A023858 15,17,19,21,23,26,29,32,35,38,20,22,24,26,29,32,35,38,41,44,47,50,53,
%U A023858 56,32,35,38,41,44,47,50,53,56,59,62,66,70,74,78,82,50,53,56,59,62,65,68,72,76,80,84,88,92
%N A023858 a(n) = 1*t(n) + 2*t(n-1) + ... + k*t(n+1-k), where k = floor((n+1)/2), t = A023531.
%F A023858 a(n) = Sum_{k=1..floor((n+1)/2)} A023531(n+1-k). - _Sean A. Irvine_, Jun 11 2019
%t A023858 Array[Sum[k Boole@ IntegerQ@ Sqrt[8 # + 9] &[# + 1 - k], {k, Floor[(# + 1)/2]}] &, 82] (* _Michael De Vlieger_, Jun 12 2019 *)
%K A023858 nonn
%O A023858 1,3
%A A023858 _Clark Kimberling_
%E A023858 Missing a(21)=10 inserted and title simplified by _Sean A. Irvine_, Jun 11 2019