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 A054015 #10 Oct 27 2023 22:00:46 %S A054015 0,0,0,0,0,2,0,0,1,1,0,0,0,0,2,2,0,0,0,1,1,1,0,0,1,0,0,2,0,6,0,0,2,1, %T A054015 0,6,0,0,1,0,0,4,0,4,2,1,0,3,1,2,2,0,0,2,1,0,1,1,0,8,0,0,0,2,0,0,0,2, %U A054015 2,3,0,1,0,0,3,3,0,5,0,6,3,1,0,7,1,0,2,0,0,0,2,0,1,1,0,1,0,2,1,4,0,1,0,0,2 %N A054015 a(n) is Chowla function of n read modulo (number of proper divisors of n), a(1) = 0 by convention. %C A054015 Chowla's function (A048050) = sum of divisors of n except 1 and n. %H A054015 Antti Karttunen, <a href="/A054015/b054015.txt">Table of n, a(n) for n = 1..16384</a> %H A054015 <a href="/index/Su#sums_of_divisors">Index entries for sequences related to sums of divisors</a> %F A054015 a(1) = 0; for n > 1, a(n) = A048050(n) mod A032741(n). %p A054015 with(numtheory): [seq((sigma(i)-i-1) mod (tau(i)-1),i=2..120);#i>1 %o A054015 (PARI) A054015(n) = if(1==n,0,((sigma(n)-n-1) % (numdiv(n)-1))); \\ _Antti Karttunen_, Oct 20 2017 %Y A054015 Cf. A032741, A048050, A054013, A054014. %K A054015 nonn %O A054015 1,6 %A A054015 _Asher Auel_, Jan 17 2000 %E A054015 Description clarified by _Antti Karttunen_, Oct 20 2017