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 A241689 Number of Sidon subsets of {1,...,n} of size 5. 0
 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 4, 22, 68, 156, 320, 584, 1008, 1622, 2520, 3734, 5428, 7612, 10488, 14126, 18744, 24390, 31436, 39914, 50212, 62390, 76932, 93918, 113960, 137058, 163896, 194632, 229988, 270018, 315712, 367106, 425220, 490164, 563080, 644096 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,12 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 EXAMPLE a(12)=4 since the only subsets of {1,...,12} satisfying the required conditions are {1,2,5,10,12}, {1,3,8,9,12}, {1,3,8,11,12}, and {1,4,5,10,12}. 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], {5}], SidonQ[#] &], {n, 1, 30}] CROSSREFS Cf. A054578. Sequence in context: A174814 A106846 A086863 * A052149 A062966 A347722 Adjacent sequences:  A241686 A241687 A241688 * A241690 A241691 A241692 KEYWORD nonn AUTHOR Carl Najafi, Apr 27 2014 STATUS approved

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Last modified December 9 07:21 EST 2021. Contains 349627 sequences. (Running on oeis4.)