%I #13 Oct 11 2013 16:49:15
%S 2,3,4,4,6,7,6,9,10,8,12,11,10,15,16,12,14,19,14,21,22,14,24,22,18,27,
%T 22,20,30,31,20,26,34,24,36,37,22,32,40,28,42,34,30,45,38,32,38,49,32,
%U 51,52,28,54,55,38,57,46,38,50,56,42,51,64,44,66,56
%N Rational knots of determinant 2n+1, counting chiral pairs twice.
%H Vincenzo Librandi, <a href="/A089266/b089266.txt">Table of n, a(n) for n = 1..1000</a>
%H A. Stoimenow, <a href="http://arxiv.org/abs/math.GT/0003172">Square numbers, spanning trees and invariants of rational knots</a> (2000)
%F a(n) = 1/2 * (A037225(n) + A034444(2*n+1)).
%t a[n_] := (EulerPhi[2*n+1] + 2^PrimeNu[2*n+1])/2; Table[a[n], {n, 1, 66}] (* _Jean-François Alcover_, Oct 11 2013, after Pari *)
%o (PARI) a(n)=(eulerphi(2*n+1)+2^omega(2*n+1))/2
%Y Cf. A078477, A078478, A018240, A051449, A051766.
%K nonn,easy,nice
%O 1,1
%A _Ralf Stephan_, Oct 30 2003