%I #7 Sep 28 2013 18:06:03

%S 1,10,13,28,31,37,40,44,49,55,59,68,71,77,89,94,97,100,104,115,119,

%T 121,139,140,142,145,148,161,166,178,181,191,196,199,205,226,232,233,

%U 238,241,248,251,259,260,262,272,274,290,293,295,301,313,314,317,329,331

%N Numbers n such that concatenation of n with 54321 is a prime.

%C Conjecture 1 : for any integer N ending in 1 or 3 or 7 or 9 there is an infinite sequence of numbers n such that the concatenation nN is a prime. Conjecture 2 : for any integer N there is an infinite sequence of numbers n such that the concatenation Nn is a prime

%H Harvey P. Dale, <a href="/A101215/b101215.txt">Table of n, a(n) for n = 1..1000</a>

%e 154321,1354321,2854321,3154321 ......... are primes

%t Select[Range[400],PrimeQ[FromDigits[Join[IntegerDigits[#],{5,4,3,2,1}]]]&] (* _Harvey P. Dale_, Sep 28 2013 *)

%K nonn,base

%O 1,2

%A _Pierre CAMI_, Dec 14 2004

%E Inserted 10, 40, 100, 260 - _R. J. Mathar_, Nov 13 2009