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 A023859 #10 Jun 13 2019 20:48:53
%S A023859 1,0,1,3,5,4,7,6,9,13,18,17,23,21,27,25,32,40,49,47,56,54,64,62,73,71,
%T A023859 82,94,107,105,119,117,132,130,145,142,158,155,172,190,209,207,227,
%U A023859 224,244,241,262,259,281,278,301,298,322,346,371,368,394,391,418,415,443,440,469,466
%N A023859 a(n) = 1*t(n) + 2*t(n-1) + ... + k*t(n+1-k), where k=floor((n+1)/2), and t = A023532.
%H A023859 Michael De Vlieger, <a href="/A023859/b023859.txt">Table of n, a(n) for n = 1..10000</a>
%t A023859 Array[Sum[k Boole@ Not@ IntegerQ@ Sqrt[8 # + 9] &[# + 1 - k], {k, Floor[(# + 1)/2]}] &, 64] (* _Michael De Vlieger_, Jun 12 2019 *)
%K A023859 nonn
%O A023859 1,4
%A A023859 _Clark Kimberling_
%E A023859 Title simplified by _Sean A. Irvine_, Jun 12 2019