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A087718 Semiprimes with greater factor less than twice the smaller factor. 3

%I

%S 4,6,9,15,25,35,49,77,91,121,143,169,187,209,221,247,289,299,323,361,

%T 391,437,493,527,529,551,589,667,703,713,841,851,899,943,961,989,1073,

%U 1147,1189,1247,1271,1333,1363,1369,1457,1517,1537,1591,1643,1681

%N Semiprimes with greater factor less than twice the smaller factor.

%C A084127(a(n)) < A084126(a(n))*2; subsequence of A001358; A001248 is a subsequence.

%C 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_, May 14 2007

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Semiprime.html">Semiprime</a>

%e 35=5*7 is a term, as 7<5*2=10;

%e 21=3*7 is not a term, as 7>3*2=6.

%K nonn

%O 1,1

%A _Reinhard Zumkeller_, Sep 29 2003

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Last modified August 29 08:06 EDT 2015. Contains 261188 sequences.