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 A215283 #20 Nov 07 2024 08:32:37
%S A215283 1,1,2,2,0,2,2,0,6,2,6,0,2,4,4,8,4,0,8,0,0,2,4,0,14,6,2,0,-2,4,8,0,2,
%T A215283 4,12,12,4,6,10,0,10,4,8,0,2,4,6,0,32,2,12,0,0,2,12,0,2,2,18,0,2,8,2,
%U A215283 32,10,8,8,0,0,4,12,0,-2,10,6,0,0,4,18,0,42
%N A215283 Row sums of triangle A215200.
%C A215283 The unsigned version of A215200 is A054521 which has as row sums the Euler totient function A000010.
%H A215283 Robert Israel, <a href="/A215283/b215283.txt">Table of n, a(n) for n = 1..10000</a>
%F A215283 a(n) = Sum_{k=1..n} (n-k | k) where (i | j) is the Kronecker symbol.
%p A215283 f:= n -> add(numtheory:-jacobi(n-k,k),k=1..n); # _Robert Israel_, Mar 11 2018
%t A215283 a[n_] := Sum[ KroneckerSymbol[n - k, k], {k, 1, n}]; Table[a[n], {n, 1, 81}] (* _Jean-François Alcover_, Jul 02 2013 *)
%o A215283 (Sage)
%o A215283 def A215200_row(n): return [kronecker_symbol(n-k, k) for k in (1..n)]
%o A215283 [sum(A215200_row(n)) for n in (1..81)]
%o A215283 (PARI) a(n) = sum(k = 1, n, kronecker(n-k, k)); \\ _Amiram Eldar_, Nov 07 2024
%Y A215283 Cf. A000010, A054521, A215200, A215284.
%K A215283 sign,look
%O A215283 1,3
%A A215283 _Peter Luschny_, Aug 07 2012