

A102946


Numbers n such that 2*10^n  7 is prime.


2



1, 2, 3, 4, 6, 16, 21, 28, 48, 82, 122, 130, 282, 304, 4602, 12984, 13614, 42762, 90597, 109928, 158242
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OFFSET

1,2


COMMENTS

Also numbers n such that 10^n + 9*R_n  6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
a(20) > 10^5.  Robert Price, Nov 16 2014
a(22) > 2*10^5.  Robert Price, Oct 25 2015


LINKS

Table of n, a(n) for n=1..21.
Makoto Kamada, Prime numbers of the form 199...993.
Index entries for primes involving repunits.


FORMULA

a(n) = A102033(n) + 1.


MAPLE

select(n > isprime(2*10^n7), [$0..10^4]); # Robert Israel, Nov 16 2014


MATHEMATICA

Do[ If[ PrimeQ[2*10^n  7], Print[n]], {n, 0, 10000}]
Select[Range[1000], PrimeQ[(2 10^#  7)] &] (* Vincenzo Librandi, Nov 17 2014 *)


PROG

(MAGMA) [n: n in [1..500]  IsPrime(2*10^n7)]; // Vincenzo Librandi, Nov 17 2014
(PARI) is(n)=ispseudoprime(2*10^n7) \\ Charles R Greathouse IV, Jun 06 2017


CROSSREFS

Cf. A002275, A102033.
Sequence in context: A280592 A002087 A049288 * A026094 A285191 A271360
Adjacent sequences: A102943 A102944 A102945 * A102947 A102948 A102949


KEYWORD

more,nonn


AUTHOR

Robert G. Wilson v, Dec 16 2004


EXTENSIONS

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
Addition of a(18)a(19) from Kamada data by Robert Price, Dec 10 2010
a(20)a(21) from Robert Price, Oct 25 2015


STATUS

approved



