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A122490 Least number k>1 such that k+10^n is a symmetric prime with symmetric digits (i.e. such that k+10^n is in A007500). 3
3, 7, 9, 7, 49, 33, 169, 7, 7, 207, 237, 91, 313, 261, 273, 79, 49, 2901, 51, 441, 193, 9, 531, 289, 1141, 67, 909, 331, 753, 2613, 657, 49, 4459, 603, 1531, 849, 2049, 259, 649, 2119, 1483, 63, 6747, 519, 3133, 937, 1159, 1999, 6921, 2949, 613, 4137, 1977, 31, 483, 883, 8553, 12117, 1009, 4347, 733 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Robert Israel, Table of n, a(n) for n = 1..722

EXAMPLE

3+10^1=13, 13 and 31 are symmetric primes with symmetric digits;

7+10^2=107, 107 and 701 are symmetric primes with symmetric digits;

9+10^3=1009, 1009 and 9001 are symmetric primes with symmetric digits.

MAPLE

revdigs:= proc(n) local L, i;

  L:= convert(n, base, 10);

  add(L[-i]*10^(i-1), i=1..nops(L))

end proc:

f:= proc(n) local k, m;

   for k from 3 by 2 do

     m:= k+10^n;

     if isprime(m) and isprime(revdigs(m)) then return k fi

   od

end proc:

map(f, [$1..100]); # Robert Israel, Nov 09 2017

CROSSREFS

Cf. A007500

Sequence in context: A113014 A102520 A275667 * A179021 A096910 A182389

Adjacent sequences:  A122487 A122488 A122489 * A122491 A122492 A122493

KEYWORD

nonn,base

AUTHOR

Pierre CAMI, Sep 16 2006

EXTENSIONS

Definition clarified, a(28) corrected, and more terms added by Robert Israel, Nov 09 2017

STATUS

approved

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Last modified October 22 04:25 EDT 2019. Contains 328315 sequences. (Running on oeis4.)