%I
%S 1,0,2,0,4,2,8,4,10,6,16,12,24,18,26,18,34,28,46,38,50,40,62,54,74,62,
%T 80,68,96,88,118,102,122,106,130,118,154,136,160,144,184,172,214,194,
%U 218,196,242,226,268,248,280,256,308,290,330,306,342,314,372,356
%N Alternating sum phi(1)  phi(2) + phi(3)  phi(4) + ... + ((1)^(n+1))*phi(n).
%F a(n) = Sum_{k=1..n} (1)^(k+1)*phi(k).
%e a(3) = phi(1)  phi(2) + phi(3) = 1  1 + 2 = 2.
%o (PARI) a068773(m)=local(s,n); s=0; for(n=1,m, if(n%2==0,s=seulerphi(n),s=s+eulerphi(n)); print1(s,","))
%Y Cf. A000010, A067929.
%K easy,nonn
%O 1,3
%A _Klaus Brockhaus_, Feb 28 2002
