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A192298 The number of sets of n positive integers strictly less than 2n such that no integer in the set divides another. 1
1, 1, 2, 3, 2, 4, 6, 6, 10, 14, 13, 26, 34, 24, 48, 72, 60, 120, 168, 168, 264, 396, 312, 624, 816, 816, 1632, 2208 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Similar to A174094, but the maximum integer in each set must be strictly less than 2n here.

LINKS

Table of n, a(n) for n=1..28.

EXAMPLE

a(1) counts {1};

a(2) counts {2,3};

a(3) counts {2,3,5} and {3,4,5};

a(4) counts {2,3,5,7}, (3,4,5,7}, and {4,5,6,7};

a(5) counts {4,5,6,7,9} and {5,6,7,8,9}.

MAPLE

with(combstruct) ;

A192298nodiv := proc(s) sl := sort(convert(s, list)) ; for i from 1 to nops(sl)-1 do for j from i+1 to nops(sl) do if op(j, sl) mod op(i, sl) = 0 then return false; end if; end do: end do:true ; end proc:

A192298 := proc(n) a := 0 ; it := iterstructs(Subset({seq(i, i=1..2*n-1)}, size=n)) :  while not finished(it) do s := nextstruct(it) ; if nops(s) = n then if A192298nodiv(s) then  a := a+1 ; end if; end if; end do: a ; end proc: # R. J. Mathar, Jul 12 2011

CROSSREFS

Cf. A174094.

Sequence in context: A244306 A345199 A079159 * A341098 A254967 A229012

Adjacent sequences:  A192295 A192296 A192297 * A192299 A192300 A192301

KEYWORD

nonn,more

AUTHOR

David Brown, Jun 27 2011

STATUS

approved

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Last modified October 28 15:26 EDT 2021. Contains 348329 sequences. (Running on oeis4.)