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 A353493 #19 Apr 27 2022 13:55:23 %S A353493 0,0,1,1,0,1,1,1,0,2,3,1,0,1,1,0,0,1,1,1,0,2,1,1,0,2,3,3,0,1,3,1,0,2, %T A353493 3,0,0,1,1,0,0,1,1,1,0,3,1,1,0,2,1,0,0,1,1,0,0,2,3,1,0,1,1,3,0,2,1,1, %U A353493 0,2,3,1,0,1,3,3,0,2,3,1,0,0,3,1,0,2,1,0,0,1,3,0,0,2,1,0,0,1,1,3,0,1,3,1,0,3 %N A353493 The arithmetic derivative of n, reduced modulo 4. %H A353493 Antti Karttunen, <a href="/A353493/b353493.txt">Table of n, a(n) for n = 0..65537</a> %F A353493 a(n) = A010873(A003415(n)). %F A353493 For all n, a(4*n) = 0 and a(4*n + 2) is either 1 or 3. [See comments in A235991] %F A353493 For all n >= 2, a(n) = A010873[(A353496(n)*A353497(n)) + A353490(n)]. (This is essentially _Reinhard Zumkeller_'s May 09 2011 recursive formula of A003415, when reduced modulo 4) - _Antti Karttunen_, Apr 26 2022 %o A353493 (PARI) %o A353493 A003415(n) = if(n<=1, 0, my(f=factor(n)); n*sum(i=1, #f~, f[i, 2]/f[i, 1])); %o A353493 A353493(n) = (A003415(n)%4); %Y A353493 Cf. A003415, A010873, A165560, A235991, A353490, A353494, A353495, A353496, A353497. %K A353493 nonn %O A353493 0,10 %A A353493 _Antti Karttunen_, Apr 22 2022