login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A087895 Primes n such that 10^n-9^n is composite. 0
5, 13, 17, 23, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

LINKS

Table of n, a(n) for n=2..57.

MATHEMATICA

Select[Prime[Range[100]], !PrimeQ[10^#-9^#]&] (* Harvey P. Dale, Jun 21 2012 *)

PROG

(PARI) apmb(a, b, n) = { forprime(x=2, n, y=a^x-b^x; if(!ispseudoprime(y), print1(x", "); ) ) }

CROSSREFS

Cf. A062576.

Primes k such that x^k - (x-1)^k is composite: A087489 (x=3), A087490 (x=4), A087685 (x=5), A087749 (x=6), A087759 (x=7), A087763 (x=8), A087894 (x=9), this sequence (x=10).

Sequence in context: A208883 A182078 A074278 * A092101 A105596 A037046

Adjacent sequences:  A087892 A087893 A087894 * A087896 A087897 A087898

KEYWORD

nonn

AUTHOR

Cino Hilliard, Oct 26 2003

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 January 23 19:45 EST 2020. Contains 331175 sequences. (Running on oeis4.)