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

 

Logo

Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing.
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A268061 Numbers n such that 7*8^n - 1 is prime. 4
3, 7, 15, 59, 6127, 8703, 11619, 23403, 124299 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(10) > 2*10^5.

Terms are A001771(n)/3 that are integers.

REFERENCES

R. K. Guy, Unsolved Problems in Theory of Numbers, Section A3.

LINKS

Table of n, a(n) for n=1..9.

H. C. Williams, The primality of certain integers of the form 2Ar^n - 1, Acta Arith. 39 (1981), 7-17.

MATHEMATICA

Select[Range[0, 200000], PrimeQ[7*8^# - 1] &]

PROG

(PARI) lista(nn) = for(n=1, nn, if(ispseudoprime(7*8^n-1), print1(n, ", "))) \\ Altug Alkan, Jan 25 2016

CROSSREFS

Cf. similar sequences of the form k*(k+1)^n-1: A003307 (k=2), ... (k=3), A046865 (k=4), A079906 (k=5), A046866 (k=6), this sequence (k=7), ... (k=8), A056725 (k=9), A046867 (k=10), A079907 (k=11).

Cf. A001771, A002235, A005541, A247260.

Sequence in context: A146448 A192169 A290470 * A298358 A023370 A181071

Adjacent sequences:  A268058 A268059 A268060 * A268062 A268063 A268064

KEYWORD

nonn,hard,more

AUTHOR

Robert Price, Jan 25 2016

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 December 9 19:51 EST 2019. Contains 329879 sequences. (Running on oeis4.)