%I A080737
%S A080737 0,0,2,2,4,2,6,4,6,4,10,4,12,6,6,8,16,6,18,6,8,10,22,6,20,12,18,8,28,6,
%T A080737 30,16,12,16,10,8,36,18,14,8,40,8,42,12,10,22,46,10,42,20,18,14,52,18,
%U A080737 14,10,20,28,58,8,60,30,12,32,16,12,66,18,24,10,70,10,72,36,22,20,16,14
%N A080737 a(1)=a(2)=0, a(2^r) = phi(2^r) (r>1), a(p^r) = phi(p^r) (p odd prime, 
               r>=1), where phi is Euler's function A000010 and in general if n 
               = Product p_i^e_i, a(n) = Sum a(p_i^e_i).
%D A080737 J. Bamberg, G. Cairns and D. Kilminster, The crystallographic restriction, 
               permutations and Goldbach's conjecture, Amer. Math. Monthly, 110 
               (March 2003), 202-209.
%o A080737 (PARI) {for(n=1,78,k=0; if(n>1,f=factor(n); k=sum(j=1,matsize(f)[1],eulerphi(f[j,
               1]^f[j,2])); if(f[1,1]==2&&f[1,2]==1,k--)); print1(k,","))}
%Y A080737 Cf. A080736, A080738, A080739, A080740, A067240.
%Y A080737 See A152455 for another version.
%Y A080737 Sequence in context: A086296 A096504 A011773 this_sequence A152455 A000010 
               A003978
%Y A080737 Adjacent sequences: A080734 A080735 A080736 this_sequence A080738 A080739 
               A080740
%K A080737 nonn,easy
%O A080737 1,3
%A A080737 N. J. A. Sloane (njas(AT)research.att.com), Mar 08 2003
%E A080737 More terms and PARI code from Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), 
               Mar 10 2003