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!)
A053409 Fibonacci numbers which are semiprimes. 13
21, 34, 55, 377, 4181, 17711, 121393, 1346269, 5702887, 165580141, 53316291173, 956722026041, 2504730781961, 308061521170129, 806515533049393, 14472334024676221, 1779979416004714189, 19740274219868223167, 573147844013817084101, 10284720757613717413913 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Subsequence of A006881, since the only square Fibonacci numbers are 1 and 144. - Charles R Greathouse IV, Sep 24 2012
Apart from a(1) = 21, all terms are of the form F(p), F(2p), or F(p^2) where F(n) is the n-th Fibonacci number. - Charles R Greathouse IV, Oct 06 2016
LINKS
FORMULA
a(n) = A000045(A072381(n)).
MATHEMATICA
Select[Fibonacci@Range[120], Last/@FactorInteger[#]=={1, 1}&] (* Vladimir Joseph Stephan Orlovsky, Jan 29 2012 *)
Select[Fibonacci[Range[150]], PrimeOmega[#]==2&] (* Harvey P. Dale, Jun 26 2020 *)
PROG
(PARI) issemi(n)=bigomega(n)==2
list(lim)=my(v=List([21]), F, t); forprime(p=2, , F=fibonacci(p); if(F>lim, break); if(issemi(F), listput(v, F))); forprime(p=2, , F=fibonacci(p^2); if(F>lim, break); if(isprime(t=fibonacci(p)) && isprime(F/t), listput(v, F))); forprime(p=2, , F=fibonacci(2*p); if(F>lim, break); if(isprime(t=fibonacci(p)) && isprime(F/t), listput(v, F))); Set(v) \\ Charles R Greathouse IV, Oct 06 2016
CROSSREFS
Column k=2 of A303216.
Sequence in context: A135595 A082483 A075735 * A253910 A144205 A261408
KEYWORD
nonn
AUTHOR
G. L. Honaker, Jr., Jan 09 2000
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 March 19 06:05 EDT 2024. Contains 370952 sequences. (Running on oeis4.)