login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A186689 Numbers n such that n^4 + 1 is a semiprime. 1
3, 5, 7, 8, 10, 11, 12, 13, 14, 17, 18, 21, 22, 23, 26, 29, 30, 32, 35, 36, 38, 39, 40, 42, 50, 52, 57, 58, 61, 62, 65, 68, 71, 72, 73, 78, 81, 84, 86, 92, 94, 98, 100, 102, 103, 105, 108, 112, 113, 114, 115, 116, 119, 120, 122, 124, 128, 129, 130, 138, 146, 148, 152, 153, 158 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Corresponding semiprimes n^4+1 are in A186688.

LINKS

Robert Price, Table of n, a(n) for n = 1..1500

EXAMPLE

3 is in the sequence because 3^4 + 1 = 82 = 2*41 is semiprime.

MATHEMATICA

SemiPrimeQ[ n_] := (n > 1) && (2 == Plus @@ (Transpose[FactorInteger[n]][[2]]));

  Select[Range[300], SemiPrimeQ[#^4 + 1] &]

Select[Range[200], PrimeOmega[#^4+1]==2&] (* Harvey P. Dale, Jan 27 2013 *)

CROSSREFS

Cf. A001358, A006313, A085722, A103854, A104238, A104335, A105041, A105066, A105078, A105122, A105142, A105237, A104479, A104494, A104657, A105282, A186688.

Sequence in context: A274140 A212294 A299495 * A186350 A189829 A175146

Adjacent sequences:  A186686 A186687 A186688 * A186690 A186691 A186692

KEYWORD

nonn

AUTHOR

Michel Lagneau, Feb 25 2011

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 20 20:46 EST 2019. Contains 329347 sequences. (Running on oeis4.)