

A068817


Numbers n such that n concatenated with n 1's is a prime.


9



1, 2, 5, 7, 10, 16, 20, 65, 91, 119, 169, 290, 428, 610, 905, 1051, 3488, 4526, 6445, 8693, 32059
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OFFSET

1,2


COMMENTS

There is no further term up to 10000.  Farideh Firoozbakht, Sep 23 2009
No more terms through 20000.  Jon E. Schoenfield, Mar 24 2018
a(22) > 50000, if it exists.  Giovanni Resta, Jun 28 2018


REFERENCES

Jason Earls, On Smarandache Repunit N Numbers, Smarandache Notions Journal (2004), Vol. 14.1, pp. 251258.


LINKS

Table of n, a(n) for n=1..21.


EXAMPLE

5 is a member as 5 followed by five 1's, 511111, is a prime.


MATHEMATICA

Do[ If[ PrimeQ[ FromDigits[ Join[IntegerDigits[n], IntegerDigits[(10^n  1)/9]]]], Print[n]], {n, 1, 1700}]


PROG

(PARI) for(n=1, 520, if(isprime(n*10^n+(10^n1)/9)==1, print1(n, ", ")))


CROSSREFS

Cf. A070220, A070746.
Sequence in context: A172410 A266594 A103871 * A156779 A345127 A226813
Adjacent sequences: A068814 A068815 A068816 * A068818 A068819 A068820


KEYWORD

nonn,base,more


AUTHOR

Amarnath Murthy, Mar 07 2002


EXTENSIONS

More terms from Benoit Cloitre, Mar 09 2002
Further terms from Vladeta Jovovic, Amarnath Murthy and Robert G. Wilson v, May 03 2002
a(17) (a probable prime) from Rick L. Shepherd, May 10 2002
a(18)a(19) (probable primes) from Jason Earls, Oct 15 2002
a(20) from Farideh Firoozbakht, Sep 23 2009
a(21) from Giovanni Resta, Jun 28 2018


STATUS

approved



