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A103300 Number of perfect rulers with length n (n>=0). 27
1, 1, 1, 2, 3, 4, 2, 12, 8, 4, 38, 30, 14, 6, 130, 80, 32, 12, 500, 326, 150, 66, 18, 4, 944, 460, 166, 56, 12, 6, 2036, 890, 304, 120, 20, 10, 2, 2678, 974, 362, 100, 36, 4, 2, 4892, 2114, 684, 238, 68, 22, 4, 16318, 6350, 2286, 836, 330, 108, 24, 12, 31980, 12252 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

For definitions, references and links related to complete rulers see A103294.

The values for n=208-213 are 22,0,0,0,4,4 according to Arch D. Robison. The values for 199-207 are not yet known. - Peter Luschny, Feb 20 2014, Jun 28 2019

Zero values at 135, 136, 149, 150, 151, 164, 165, 166, 179, 180, 181, 195, 196, 209, 210, 211. - Ed Pegg Jr, Jun 23 2019 [These values were found by Arch D. Robison, see links. Peter Luschny, Jun 28 2019]

LINKS

Peter Luschny (0..123) and Arch D. Robison (124..198), Table of n, a(n) for n = 0..198

Peter Luschny, Perfect and Optimal Rulers.

Arch D. Robison, Parallel Computation of Sparse Rulers, Jan 14 2014.

Index entries for sequences related to perfect rulers.

FORMULA

a(n) = T(n, A103298(n)) where the triangle T is described by A103294.

EXAMPLE

a(5)=4 counts the perfect rulers with length 5, {[0,1,3,5],[0,2,4,5],[0,1,2,5],[0,3,4,5]}.

CROSSREFS

Cf. A004137 (Maximal number of edges in a graceful graph on n nodes).

Cf. A103301, A103297, A103298.

Sequence in context: A220335 A117009 A204842 * A305402 A213394 A237981

Adjacent sequences:  A103297 A103298 A103299 * A103301 A103302 A103303

KEYWORD

nonn,nice

AUTHOR

Peter Luschny Feb 28 2005

STATUS

approved

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Last modified October 23 19:59 EDT 2019. Contains 328373 sequences. (Running on oeis4.)