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 A345036 #16 Jun 07 2021 09:10:16
%S A345036 1,-1,11,-66,623,-7743,117695,-2097676,43046069,-999989915,
%T A345036 25937439347,-743008621122,23298084749141,-793714765727191,
%U A345036 29192926036832303,-1152921504875220776,48661191875256608663,-2185911559727678466189,104127350297928222613599
%N A345036 a(n) = Sum_{k=1..n} (-n)^(floor(n/k) - 1).
%H A345036 Seiichi Manyama, <a href="/A345036/b345036.txt">Table of n, a(n) for n = 1..387</a>
%F A345036 a(n) = [x^n] (1/(1 - x)) * Sum_{k>=1} x^k * (1 - x^k)/(1 + n*x^k).
%t A345036 a[n_] := Sum[(-n)^(Floor[n/k] - 1), {k, 1, n}]; Array[a, 20] (* _Amiram Eldar_, Jun 06 2021 *)
%o A345036 (PARI) a(n) = sum(k=1, n, (-n)^(n\k-1));
%Y A345036 Diagonal of A345033.
%Y A345036 Cf. A344820, A345030, A345037.
%K A345036 sign
%O A345036 1,3
%A A345036 _Seiichi Manyama_, Jun 06 2021