Search: id:A078644
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%I A078644
%S A078644 1,2,3,3,3,6,3,4,5,6,3,9,3,6,9,5,3,10,3,9,9,6,3,12,5,6,7,9,3,18,3,6,9,
               6,
%T A078644 9,15,3,6,9,12,3,18,3,9,15,6,3,15,5,10,9,9,3,14,9,12,9,6,3,27,3,6,15,7,
%U A078644 9,18,3,9,9,18,3,20,3,6,15,9,9,18,3,15,9,6,3,27,9,6,9,12,3,30,9,9,9,6,
               9
%N A078644 a(n) = tau(2*n^2)/2.
%C A078644 Inverse Moebius transform of A068068. Number of elements in the set {(x,
               y): x is odd, x|n, y|n, gcd(x,y)=1}.
%C A078644 The number of Pythagorean points (x,y), 0<x<y, located on the hyperbola 
               y=2n(x-n)/(x-2n) and having "excess" x+y-z = 2n. - Seppo Mustonen 
               (seppo.mustonen(AT)helsinki.fi), Jun 07 2005
%C A078644 a(n) is the number of Pythagorean triangles with radius of the inscribed 
               circle equal to n. - Ant King, mathstutoring(AT)ntlworld.com, Mar 
               06 2006. For number of primitive Pythagorean triangles having inradius 
               n, see A068068(n).
%H A078644 S. Mustonen, <a href="http://www.survo.fi/papers/pythagorean.pdf">Visualization 
               and characterization of Pythagorean triples</a>
%F A078644 Multiplicative with a(2^e) = e+1, a(p^e) = 2*e+1, p>2. a(n) = tau(n^2) 
               if n is odd, a(n) = tau(n^2)-a(n/2) if n is even.
%Y A078644 Cf. A000005, A048691.
%Y A078644 Sequence in context: A126868 A119688 A134187 this_sequence A133700 A087688 
               A126854
%Y A078644 Adjacent sequences: A078641 A078642 A078643 this_sequence A078645 A078646 
               A078647
%K A078644 mult,nonn
%O A078644 1,2
%A A078644 Vladeta Jovovic (vladeta(AT)eunet.rs), Dec 13 2002

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