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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A246804 Numbers k such that (10^(k+2) + 999) * 10^k + 1 is prime. 1
1, 3, 15, 135, 645, 1373, 195317, 237249 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Or, indices of primes in the sequence of decimal palindromes 19991, 1099901, 100999001, 10009990001, ...

Or, numbers k such that there exists an "upside-down-Belphegor's primes" of length 2*k+3.

LINKS

Table of n, a(n) for n=1..8.

MAPLE

A246804:=n->`if`(isprime((10^(n+2)+999)*10^n+1), n, NULL): seq(A246804(n), n=1..10^3); # Wesley Ivan Hurt, Nov 16 2014

MATHEMATICA

Select[Range[10^3], PrimeQ[(10^(# + 2) + 999)*10^# + 1] &]

PROG

(PARI) for( n=1, 9999, ispseudoprime((10^(n+2)+999)*10^n+1) & print1(n", "))

(MAGMA) [n: n in [1..500] | IsPrime((10^(n+2)+999)*10^n+1)];

CROSSREFS

Cf. A156166 (Belphegor's primes), A082703 (plateau primes 199...991).

Sequence in context: A108210 A006717 A222263 * A230166 A059861 A232699

Adjacent sequences:  A246801 A246802 A246803 * A246805 A246806 A246807

KEYWORD

nonn,more,base,hard

AUTHOR

Serge Batalov, Nov 16 2014

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 May 6 01:51 EDT 2021. Contains 343579 sequences. (Running on oeis4.)