0,9

If n=k then T(n,k)=1.

A ruler is a strict increasing finite sequence of marks (nonnegative integers).

A segment of a ruler is the space between two adjacent marks. The number of segments is the number of marks - 1.

A ruler is complete if the set of all distances it can measure is {1,2,3,...,k} for some integer k>=1.

A ruler is perfect if it is complete and no complete ruler with the same length possesses less marks.

A ruler is optimal if it is perfect and no perfect ruler with the same number of segments has a greater length.

The 'empty ruler' with length n=0 is considered perfect and optimal.

R. K. Guy, Modular difference sets and error correcting codes. in: Unsolved Problems in Number Theory, 3rd ed. New York: Springer-Verlag, chapter C10, pp. 181-183, 2004.

J. C. P. Miller, Difference bases: Three problems in additive number theory, pp. 299-322 of A. O. L. Atkin and B. J. Birch, editors, Computers in Number Theory. Academic Press, NY, 1971.

B. Wichmann. A note on restricted difference bases. J. London Math.Soc. 38, 1962, 465-466

Peter Luschny, Perfect and Optimal Rulers.

Peter Luschny, Table of Counts.

Eric Weisstein's World of Mathematics, Perfect Ruler.

Index entries for sequences related to perfect rulers.

Rows begin:

[1],

[0,1],

[0,0,1],

[0,0,2,1],

[0,0,0,3,1],

[0,0,0,4,4,1],

[0,0,0,2,9,5,1],

[0,0,0,0,12,14,6,1],

[0,0,0,0,8,27,20,7,1],...

a(19)=T(5,4)=4 counts the complete rulers with length 5 and 4 segments: {[0,2,3,4,5],[0,1,3,4,5],[0,1,2,4,5],[0,1,2,3,5]}

Row sums give A103295. Column sums give A103296. The first nonzero entries in the rows give A103300.

The last nonzero entries in the columns give A103299. The row numbers of the last nonzero entries in the columns give A004137.

Cf. A103295 through A103301, A004137.

Sequence in context: A106278 A064287 A128206 this_sequence A079680 A037855 A037873

Adjacent sequences: A103291 A103292 A103293 this_sequence A103295 A103296 A103297

nonn,tabl

Peter Luschny (peter(AT)luschny.de) Feb 28 2005