

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
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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



