%I A002180 M0500 N0180
%S A002180 1,2,3,4,5,6,8,9,10,11,12,14,15,16,18,20,21,22,23,24,26,27,28,29,
%T A002180 30,32,33,35,36,39,40,41,42,44,46,48,50,51,52,53,54,55,56,58,60,
%U A002180 63,64,65,66,68,69,70,72,74,75,78,80,81,82,83,84,86,88,89,90,92
%N A002180 Values taken by the half-totient function phi(m)/2.
%D A002180 M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, 
               National Bureau of Standards Applied Math. Series 55, 1964 (and various 
               reprintings), p. 840.
%D A002180 J. W. L. Glaisher, Number-Divisor Tables. British Assoc. Math. Tables, 
               Vol. 8, Camb. Univ. Press, 1940, p. 64.
%D A002180 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A002180 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%H A002180 T. D. Noe, <a href="b002180.txt">Table of n, a(n) for n=2..10000</a>
%H A002180 M. Abramowitz and I. A. Stegun, eds., <a href="http://www.nrbook.com/
               abramowitz_and_stegun/">Handbook of Mathematical Functions</a>, National 
               Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972 
               [alternative scanned copy].
%F A002180 a(n) = A002202(n)/2 for n>1.
%p A002180 with(numtheory); t1 := [seq(nops(invphi(n)), n=1..300)]; t2 := []: for 
               n from 2 to 300 do if t1[n] <> 0 then t2 := [op(t2), n/2]; fi; od: 
               t2;
%Y A002180 Cf. A002202.
%Y A002180 Sequence in context: A114024 A030173 A048265 this_sequence A102799 A059519 
               A163101
%Y A002180 Adjacent sequences: A002177 A002178 A002179 this_sequence A002181 A002182 
               A002183
%K A002180 nonn,nice,easy
%O A002180 2,2
%A A002180 N. J. A. Sloane (njas(AT)research.att.com).
%E A002180 More terms from Barbara Haas Margolius (margolius(AT)math.csuohio.edu) 
               2/12/01