%I A062570
%S A062570 1,2,2,4,4,4,6,8,6,8,10,8,12,12,8,16,16,12,18,16,12,20,22,16,20,24,18,
%T A062570 24,28,16,30,32,20,32,24,24,36,36,24,32,40,24,42,40,24,44,46,32,42,40,
%U A062570 32,48,52,36,40,48,36,56,58,32,60,60,36,64,48,40,66,64,44,48,70,48,72
%N A062570 phi(2*n).
%C A062570 a(n) is also the number of non-congruent solutions to x^2 - y^2 = 1 mod 
               n. - Yuval Dekel (dekelyuval(AT)hotmail.com), Sep 21 2003
%F A062570 a(n) = Sum_{d divides n and d is odd} n/d*mu(d). Multiplicative with 
               a(2^e) = 2^e and a(p^e) = p^e-p^(e-1), p>2. - Vladeta Jovovic (vladeta(AT)eunet.rs), 
               Dec 04 2002
%F A062570 Dirichlet g.f.: zeta(s-1)/zeta(s)*2^s/(2^s-1). - Ralf Stephan, Jun 17 
               2007
%o A062570 (PARI) a(n)=if(n<1,0,eulerphi(2*n))
%o A062570 (Other) sage: [euler_phi(2*n)for n in xrange(1,74)]# [From Zerinvary 
               Lajos (zerinvarylajos(AT)yahoo.com), Jun 06 2009]
%Y A062570 Cf. A000010, A008683. a(n)=A000010(2n).
%Y A062570 Cf. A062803, A060968.
%Y A062570 Sequence in context: A085237 A110870 A035114 this_sequence A108514 A120456 
               A115383
%Y A062570 Adjacent sequences: A062567 A062568 A062569 this_sequence A062571 A062572 
               A062573
%K A062570 mult,nonn
%O A062570 1,2
%A A062570 Jason Earls (zevi_35711(AT)yahoo.com), Jul 03 2001
%E A062570 Corrected by Vladeta Jovovic (vladeta(AT)eunet.rs), Dec 04 2002