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A241690 Number of Sidon subsets of {1,...,n} of size 6. 0
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 24, 80, 206, 504, 1004, 1910, 3380, 5688, 9036, 14106, 21190, 31158, 44370, 62206, 85308, 115662, 153746, 202146, 262156, 336960, 427488, 538690, 671604, 831926, 1021238, 1246604, 1510056, 1820580, 2179480 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,18

COMMENTS

A Sidon set is a set of natural numbers A={a_1,a_2,...}, finite or infinite, such that all pairwise sums a_i+a_j (i <= j) are different.

LINKS

Table of n, a(n) for n=1..47.

EXAMPLE

a(18)=8 since there are 8 subsets of {1,...,18} satisfying the required conditions, for example {1,2,5,11,13,18}.

MATHEMATICA

SidonQ[l__] := If[Length[Join[Plus @@@ Subsets[l, {2}], 2 l]] == Length[Union[Join[Plus @@@ Subsets[l, {2}], 2 l]]], True, False]

Table[Length@Select[Subsets[Range[n], {6}], SidonQ[#] &], {n, 1, 30}]

CROSSREFS

Cf. A054578.

Sequence in context: A221906 A116486 A179609 * A141317 A146534 A180888

Adjacent sequences:  A241687 A241688 A241689 * A241691 A241692 A241693

KEYWORD

nonn

AUTHOR

Carl Najafi, Apr 27 2014

STATUS

approved

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Last modified October 27 19:53 EDT 2021. Contains 348288 sequences. (Running on oeis4.)