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A028989 Smallest palindromic prime with 2n-1 digits. 2
2, 101, 10301, 1003001, 100030001, 10000500001, 1000008000001, 100000323000001, 10000000500000001, 1000000008000000001, 100000000212000000001, 10000000000300000000001 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..500

P. De Geest, World!Of Palindromic Primes

MATHEMATICA

t={}; Do[p=NextPrime[10^(2*n)]; While[Reverse[x=IntegerDigits[p]]!=x, p=NextPrime[p]]; AppendTo[t, p], {n, 0, 6}]; t (* Jayanta Basu, Jun 05 2013 *)

PROG

(PARI) a(n)={

n--;

my(N=100^n+1, aS=10^(n+3)+10^(n-3), bS=10^(n+2)+10^(n-2), cS=10^(n+1)+10^(n-1), dS=10^n);

forstep(a=N, N+9*aS, aS,

forstep(b=a, a+9*bS, bS,

forstep(c=b, b+9*cS, cS,

forstep(d=c, c+9*dS, dS,

if(ispseudoprime(d), return(d))

))));

warning("could not find a("n")")

}; \\ Charles R Greathouse IV, Feb 15 2011

CROSSREFS

Sequence in context: A072383 A222449 A035325 * A113575 A173640 A111012

Adjacent sequences:  A028986 A028987 A028988 * A028990 A028991 A028992

KEYWORD

nonn,base

AUTHOR

Patrick De Geest

EXTENSIONS

a(10) corrected by Farideh Firoozbakht, Oct 10, 2005

STATUS

approved

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Last modified August 30 10:35 EDT 2014. Contains 246218 sequences.