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 A243046 #17 Jan 21 2025 18:20:33 %S A243046 0,0,1,1,0,2,0,1,1,1,0,5,0,0,3,1,0,2,0,2,2,0,0,7,0,0,1,2,0,5,0,1,1,0, %T A243046 1,6,0,0,1,4,0,4,0,1,4,0,0,7,0,1,1,1,0,2,1,2,1,0,0,13,0,0,3,1,0,3,0,1, %U A243046 1,2,0,8,0,0,3,1,0,3,0,4,1,0,0,10,0,0,1,1,0,7,1,1,1,0,0,7,0,0,2 %N A243046 Number of solutions to k*n/(k+n) = x and k*n/(k-n) = y for integers x and y and natural number k. %C A243046 Question: Is there any direct formula for this sequence? Cf. for example A146564. - _Antti Karttunen_, Feb 18 2023 %H A243046 Antti Karttunen, <a href="/A243046/b243046.txt">Table of n, a(n) for n = 1..10080</a> %F A243046 a(n) <= A063647(n), a(n) <= A146564(n). - _Antti Karttunen_, Feb 18 2023 %e A243046 6*k/(k-6) and 6*k/(k+6) are integers for k = 3 (-6 and 2, respectively) and k = 12 (12 and 4, respectively). Thus a(6) = 2. %o A243046 (PARI) A243046(n) = sum(k=1, n*(n+1), (k!=n && !((k*n)%(k+n)) && !((k*n)%(k-n)))); \\ [improved by _Antti Karttunen_, Feb 18 2023] %Y A243046 Cf. A063647, A146564, A243017, A243045, A243047 (positions of 0's), A360120 (their characteristic function). %K A243046 nonn %O A243046 1,6 %A A243046 _Derek Orr_, May 29 2014