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 A215285 #13 Nov 08 2024 07:20:09
%S A215285 1,2,3,4,6,9,16,36,64,100,144,196,256,324,400,484,576,676,784,900,
%T A215285 1024,1156,1296,1444,1600,1764,1936,2116,2304,2500,2704,2916,3136,
%U A215285 3364,3600,3844,4096,4356,4624,4900,5184,5476,5776,6084,6400,6724,7056,7396,7744
%N A215285 Numbers m such that Sum_{k=1..m} (m - k | k) = phi(m), where (i|j) is the Kronecker symbol and phi(m) is the Euler totient function.
%C A215285 n is in this sequence if and only if sum_{k=1..n} (n-k|k) = sum_{k=1..n} |(n-k|k)|.
%H A215285 Amiram Eldar, <a href="/A215285/b215285.txt">Table of n, a(n) for n = 1..500</a>
%t A215285 Reap[ Do[ If[ Sum[ KroneckerSymbol[n - k, k], {k, 1, n}] == EulerPhi[n], Print[n]; Sow[n]], {n, 1, 8000}]][[2, 1]] (* _Jean-François Alcover_, Jul 29 2013 *)
%o A215285 (Sage)
%o A215285 def A215200_row(n): return [kronecker_symbol(n-k, k) for k in (1..n)]
%o A215285 [n for n in (1..1000) if sum(A215200_row(n)) == euler_phi(n)]
%o A215285 (PARI) is(m) = sum(k = 1, m, kronecker(m-k, k)) == eulerphi(m); \\ _Amiram Eldar_, Nov 08 2024
%Y A215285 Cf. A000010, A215200, A215283, A215284.
%K A215285 nonn
%O A215285 1,2
%A A215285 _Peter Luschny_, Aug 07 2012