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A384218

Numbers k such that the concatenations of k and 123456789 in both orders are prime.

217, 409, 629, 653, 779, 871, 881, 1091, 1463, 1489, 1913, 1993, 2039, 2729, 2881, 3397, 3649, 3677, 3751, 3961, 4073, 4321, 4843, 4961, 5039, 5507, 5609, 5683, 5849, 5941, 6593, 6613, 6713, 6923, 7349, 7571, 7789, 7907, 8413, 8419, 8617, 8623, 8687, 8689, 8797, 8909, 9083, 9589, 9973, 10241

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OFFSET

1,1

COMMENTS

Numbers k such that both concatenations k123456789 and 123456789k are prime.

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

EXAMPLE

a(3) = 629 is a term because 629123456789 and 123456789629 are prime.

MAPLE

filter:= proc(n) isprime(n*10^9+123456789) and

isprime(123456789*10^(1+ilog10(n))+n) end proc;