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Number of pairs (x,y) 1<=x<=y<=n such that 1/x+1/y+1/n > 1/2.
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%I #5 Mar 30 2012 18:39:11

%S 1,3,6,10,15,20,24,26,29,30,33,34,36,37,38,40,42,43,45,46,48,50,52,53,

%T 55,57,59,61,63,65,67,69,71,73,75,77,79,81,83,85,87,88,90,92,94,96,98,

%U 100,102,104,106,108,110,112,114,116,118,120,122,124,126,128,130,132

%N Number of pairs (x,y) 1<=x<=y<=n such that 1/x+1/y+1/n > 1/2.

%F for n>=43 a(n) = 2n-4

%o (PARI) a(n)=sum(i=1,n,sum(j=1,i,if(sign(1/i+1/j+1/n-1/2)-1,0,1)))

%K nonn

%O 1,2

%A _Benoit Cloitre_, Dec 08 2002