A268061 - OEIS

A268061

Numbers k such that 7*8^k - 1 is prime.

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

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).

KEYWORD

nonn,hard,more

AUTHOR

Robert Price, Jan 25 2016

STATUS

approved