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A242605
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Start of a triple of consecutive squarefree numbers which are all semiprimes.
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6
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33, 55, 85, 91, 93, 115, 118, 119, 141, 142, 143, 158, 201, 202, 203, 205, 213, 214, 215, 217, 218, 295, 298, 299, 301, 302, 323, 326, 391, 393, 411, 413, 445, 451, 511, 514, 535, 542, 551, 622, 633, 685, 694, 695, 697, 745, 763, 778, 791, 799, 815, 842, 843, 865, 898, 921, 922
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OFFSET
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1,1
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COMMENTS
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LINKS
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EXAMPLE
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33 is in the sequence because 33, 34, 35 are all squarefree semiprimes.
55 is in the sequence because 55, 57, 58 (we ignore 56 because it's not squarefree) are all squarefree semiprimes.
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MATHEMATICA
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Transpose[Select[Partition[Select[Range[1000], SquareFreeQ], 3, 1], Union[ PrimeOmega[ #]] =={2}&]][[1]] (* Harvey P. Dale, Feb 07 2016 *)
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PROG
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(PARI) is_A242605(n, c=2)==issquarefree(n)&&omega(n)==2&&(!c||until(issquarefree(n++), )||is_A242605(n, c-1))
(PARI) (back(n, c=1)=until(issquarefree(n--)&&c--, ); n); for(n=1, 999, issquarefree(n)||next; dk==4&&dk==dm&&numdiv(n)==dm&&print1(back(n)", "); dk=dm; dm=numdiv(n))
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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