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

 

Logo

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 59th year, we have over 358,000 sequences, and we’ve crossed 10,300 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A227576 Numbers n such that F(3*n)/(2*F(n)) is prime, where F(k) is the k-th Fibonacci number. 1
5, 7, 11, 13, 17, 31, 37, 41, 67, 107, 151, 257, 349, 457, 787, 911, 1289, 1627, 3271, 8233, 13163, 14551, 31517, 55579 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

All terms are primes. Conjecture: this sequence is infinite.

LINKS

Table of n, a(n) for n=1..24.

EXAMPLE

For n = 5 we have F(3*5)/(2*F(5)) = F(15)/(2*5) = 610/10 = 61 is prime.

MATHEMATICA

Select[Range[1000], PrimeQ[Fibonacci[3*#]/Fibonacci[#]/2] &] (* Vaclav Kotesovec, Jul 18 2013 *)

PROG

(PARI) forprime(p=5, 1e4, if(ispseudoprime(t=fibonacci(3*p)/fibonacci(p) /2), print1(p", "))) \\ Charles R Greathouse IV, Jul 16 2013

(PFGW) ABC2 F(3*$a)/2/F($a)

a: primes from 5 to 25000

// Charles R Greathouse IV, Jul 16 2013

CROSSREFS

Cf. A001605, A000045, A227627.

Sequence in context: A109416 A132170 A106309 * A114262 A255229 A230217

Adjacent sequences: A227573 A227574 A227575 * A227577 A227578 A227579

KEYWORD

nonn,more

AUTHOR

Thomas Ordowski, Jul 16 2013

EXTENSIONS

a(6)-a(22) from Charles R Greathouse IV, Jul 16 2013

a(23) from Vaclav Kotesovec, Jul 18 2013

a(24) from Charles R Greathouse IV, Jul 18 2013

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 November 27 14:41 EST 2022. Contains 358405 sequences. (Running on oeis4.)