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A087718
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Semiprimes with greater factor less than twice the smaller factor.
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3
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4, 6, 9, 15, 25, 35, 49, 77, 91, 121, 143, 169, 187, 209, 221, 247, 289, 299, 323, 361, 391, 437, 493, 527, 529, 551, 589, 667, 703, 713, 841, 851, 899, 943, 961, 989, 1073, 1147, 1189, 1247, 1271, 1333, 1363, 1369, 1457, 1517, 1537, 1591, 1643, 1681
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| A084127(a(n)) < A084126(a(n))*2; subsequence of A001358; A001248 is a subsequence.
Odd composite integers which do not have a representation as the sum of an even number of consecutive integers. For instance, 27 is not in the sequence because it has a representation as the sum of an even number of consecutive integers (2+3+4+5+6+7). 35 is in the sequence because it does not have such a representation. - Andrew Plewe (aplewe(AT)sbcglobal.net), May 14 2007
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LINKS
| Eric Weisstein's World of Mathematics, Semiprime
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EXAMPLE
| 35=5*7 is a term, as 7<5*2=10;
21=3*7 is not a term, as 7>3*2=6.
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CROSSREFS
| Sequence in context: A116589 A118688 A118691 * A033476 A183978 A118696
Adjacent sequences: A087715 A087716 A087717 * A087719 A087720 A087721
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KEYWORD
| nonn
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AUTHOR
| Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Sep 29 2003
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