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A206778
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Irregular triangle in which n-th row lists squarefree divisors (A005117) of n.
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16
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1, 1, 2, 1, 3, 1, 2, 1, 5, 1, 2, 3, 6, 1, 7, 1, 2, 1, 3, 1, 2, 5, 10, 1, 11, 1, 2, 3, 6, 1, 13, 1, 2, 7, 14, 1, 3, 5, 15, 1, 2, 1, 17, 1, 2, 3, 6, 1, 19, 1, 2, 5, 10, 1, 3, 7, 21, 1, 2, 11, 22, 1, 23, 1, 2, 3, 6, 1, 5, 1, 2, 13, 26, 1, 3, 1, 2, 7, 14, 1, 29
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OFFSET
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1,3
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LINKS
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EXAMPLE
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Triangle begins:
. 1: [1]
. 2: [1, 2]
. 3: [1, 3]
. 4: [1, 2]
. 5: [1, 5]
. 6: [1, 2, 3, 6]
. 7: [1, 7]
. 8: [1, 2]
. 9: [1, 3]
. 10: [1, 2, 5, 10]
. 11: [1, 11]
. 12: [1, 2, 3, 6].
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MAPLE
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local sqdvs , nfac, d;
sqdvs := {} ;
nfac := ifactors(n)[2] ;
for d in numtheory[divisors](n) do
if issqrfree(d) then
sqdvs := sqdvs union {d} ;
end if;
end do:
sort(sqdvs) ;
end proc:
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MATHEMATICA
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Flatten[Table[Select[Divisors[n], SquareFreeQ], {n, 30}]] (* Harvey P. Dale, Apr 11 2012 *)
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PROG
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(Haskell)
a206778 n k = a206778_row n !! k
a206778_row = filter ((== 1) . a008966) . a027750_row
a206778_tabf = map a206778_row [1..]
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CROSSREFS
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KEYWORD
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nonn,tabf
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AUTHOR
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STATUS
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approved
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