%I A002472 M0411 N0157
%S A002472 1,1,1,2,3,1,5,4,3,3,9,2,11,5,3,8,15,3,17,6,5,9,21,4,15,11,9,10,27,3,29,
%T A002472 16,9,15,15,6,35,17,11,12,39,5,41,18,9,21,45,8,35,15,15,22,51,9,27,20,
               17,
%U A002472 27,57,6,59,29,15,32,33,9,65,30,21,15,69,12,71,35,15,34,45,11,77,24,27
%N A002472 Number of pairs x,y such that y-x=2, (x,n)=1, (y,n)=1 and 1 <= x <= n.
%D A002472 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A002472 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A002472 Golubev, V. A.; Nombres de Mersenne et caracteres du nombre 2. Mathesis 
               67 1958 257-262.
%H A002472 T. D. Noe, <a href="b002472.txt">Table of n, a(n) for n=1..1000</a>
%F A002472 Multiplicative with a(p^e) = p^(e-1) if p = 2; (p-2)*p^(e-1) if p > 2. 
               - David W. Wilson (davidwwilson(AT)comcast.net), Aug 01, 2001.
%Y A002472 Sequence in context: A047706 A114711 A166285 this_sequence A060116 A114690 
               A049274
%Y A002472 Adjacent sequences: A002469 A002470 A002471 this_sequence A002473 A002474 
               A002475
%K A002472 nonn,nice,easy,mult
%O A002472 1,4
%A A002472 N. J. A. Sloane (njas(AT)research.att.com).
%E A002472 More terms from David W. Wilson (davidwwilson(AT)comcast.net)