This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A205728 Number of odd, nonsquare semiprimes <= n^2. 2
 0, 0, 0, 1, 2, 4, 5, 8, 11, 16, 19, 24, 28, 32, 41, 46, 50, 60, 66, 73, 81, 89, 100, 110, 118, 126, 140, 151, 163, 174, 187, 197, 210, 224, 239, 253, 269, 286, 298, 312, 326, 344, 363, 380, 399, 414, 435, 451, 468, 491, 513, 530, 546, 567, 591, 619, 643, 664 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,5 COMMENTS Like A205727 (see comments thereto), this looks at odd semiprimes, but excludes squares.  This then relates to the Goldbach conjecture 2j=p+q with the additional restriction that j, p, and q are not equal. LINKS MATHEMATICA SemiPrimeQ[n_Integer] := If[Abs[n] < 2, False, (2 == Plus @@ Transpose[FactorInteger[Abs[n]]][[2]])]; nn = 100;  t = Select[Range[1, nn^2, 2], SemiPrimeQ[#] && ! IntegerQ[Sqrt[#]] &]; Table[Length[Select[t, # <= n^2 &]], {n, nn}] (* T. D. Noe, Jan 30 2012 *) CROSSREFS Cf. A205726, A205727. Sequence in context: A222044 A175106 A216566 * A074824 A039867 A182564 Adjacent sequences:  A205725 A205726 A205727 * A205729 A205730 A205731 KEYWORD nonn AUTHOR Keith Backman, Jan 30 2012 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Puzzles | Hot | Classics
Recent Additions | More pages | Superseeker | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .