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A156166 Numbers k > 0 such that (10^(k+2) + 666)*10^k + 1 is prime. 4
1, 14, 43, 507, 609, 2473, 2624, 28292, 181299 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
Or, indices of primes in the sequence 16661, 1066601, 100666001, 10006660001,... Ondrejka calls these "beastly palindromic primes".
In popular culture: the number generated by a(2), 1000000000000066600000000000001, also known as Belphegor's Prime, was used as a plot device in Episode "Just a Regular Irregular" of the "Elementary" TV series (first aired Nov/13/2014). - Serge Batalov, Nov 15 2014
LINKS
Eric Weisstein's World of Mathematics, Belphegor Prime
Eric Weisstein's World of Mathematics, Integer Sequence Primes
FORMULA
a(n) = A232448(n) + 1.
MAPLE
A156166:=n->`if`(isprime((10^(n+2)+666)*10^n+1), n, NULL): seq(A156166(n), n=1..10^3); # Wesley Ivan Hurt, Nov 16 2014
MATHEMATICA
Select[Range[10^3], PrimeQ[(10^(# + 2) + 666)*10^# + 1] &] (* Arkadiusz Wesolowski, Sep 08 2011 *)
PROG
(PARI) for( n=1, 9999, ispseudoprime((10^(n+2)+666)*10^n+1) & print1(n", "))
(Magma) [n: n in [1..500] | IsPrime((10^(n+2)+666)*10^n+1)]; // Vincenzo Librandi, Nov 15 2014
CROSSREFS
Cf. A082700 and search results for 16661.
Cf. A232448 (a(n) - 1).
Sequence in context: A302665 A041380 A151990 * A064125 A089031 A265152
KEYWORD
more,nonn,base
AUTHOR
M. F. Hasler, Feb 10 2009
EXTENSIONS
a(8) = 28292 (discovered on Jan 05 2004, by Daniel Heuer), Arkadiusz Wesolowski, Mar 16 2011
a(9) = 181299 from Serge Batalov, Nov 15 2014
STATUS
approved

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Last modified April 24 22:17 EDT 2024. Contains 371964 sequences. (Running on oeis4.)