login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A103392 Semiprimes in A103372. 6
4, 9, 15, 21, 33, 38, 58, 86, 106, 122, 485, 905, 1939, 4163, 6697, 12381, 14473, 22889, 107833, 170769, 370729, 687634, 804106, 1093762, 1276259, 2767999, 11140379, 15186449, 210634829, 286937249, 391048473, 532793518, 725995178, 847539571 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Intersection of A103372 with A001358.
LINKS
EXAMPLE
276799 is an element of this sequence because A103372(99) = 276799 and 276799 is semiprime because 276799 = 31 * 8929 where both 31 and 8929 are primes.
MATHEMATICA
SemiprimeQ[n_] := Plus @@ FactorInteger[n][[All, 2]] == 2; k = 4; Do[a[n] = 1, {n, k + 1}]; a[n_] := a[n] = a[n - k] + a[n - k - 1]; Union[Select[Array[a, 150], SemiprimeQ]]
Union[Select[LinearRecurrence[{0, 0, 0, 1, 1}, {1, 1, 1, 1, 1}, 150], PrimeOmega[#] == 2&]] (* Harvey P. Dale, Apr 22 2015 *)
CROSSREFS
Sequence in context: A103394 A103395 A103393 * A073046 A066495 A313298
KEYWORD
nonn,easy
AUTHOR
Jonathan Vos Post, Feb 03 2005
EXTENSIONS
Edited, corrected and extended by Ray Chandler and Robert G. Wilson v, Feb 06 2005
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified April 19 14:10 EDT 2024. Contains 371792 sequences. (Running on oeis4.)