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Number of triples {i,j,k}, i>1, j>1, k>1, such that ijk < n^3.
2

%I #8 Sep 02 2013 09:43:44

%S 0,7,35,104,238,482,851,1402,2147,3179,4497,6210,8324,10921,14048,

%T 17759,22146,27247,33158,39953,47652,56372,66135,77187,89351,102902,

%U 117801,134252,152148,171853,193328,216471,241557,268780,298017,329515

%N Number of triples {i,j,k}, i>1, j>1, k>1, such that ijk < n^3.

%F sum(sum(floor((n^3-1)/(ij))-j+1, j=i..floor(sqrt((n^3-1)/i))), i=2..n-1).

%e f(3)=7 because the only triples ijk < 27 are (2,2,2) (2,2,3) (2,2,4) (2,2,5) (2,2,6) (2,3,3) (2,3,4).

%o (PARI) a(n) = sum(i = 2, n-1, sum(j = i, floor(sqrt((n^3-1)/i)), floor((n^3-1)/(i*j))-j+1)); \\ _Michel Marcus_, Sep 02 2013

%Y Cf. A037048.

%K nonn

%O 2,2

%A Joe K. Crump (joecr(AT)carolina.rr.com)