A037092 Number of triples {i,j,k}, i>1, j>1, k>1, such that ijk < n^3.

0, 7, 35, 104, 238, 482, 851, 1402, 2147, 3179, 4497, 6210, 8324, 10921, 14048, 17759, 22146, 27247, 33158, 39953, 47652, 56372, 66135, 77187, 89351, 102902, 117801, 134252, 152148, 171853, 193328, 216471, 241557, 268780, 298017, 329515

Offset

2,2

Links

Table of n, a(n) for n=2..37.

Formula

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

Example

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).

Prog

(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

Crossrefs

Cf. A037048.

Sequence in context: A152744 A169607 A130884 * A210368 A015667 A206723

Adjacent sequences: A037089 A037090 A037091 * A037093 A037094 A037095

Keyword

nonn

Author

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

Status

approved