OFFSET
1,2
COMMENTS
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
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
154321,1354321,2854321,3154321 ......... are primes
MATHEMATICA
Select[Range[400], PrimeQ[FromDigits[Join[IntegerDigits[#], {5, 4, 3, 2, 1}]]]&] (* Harvey P. Dale, Sep 28 2013 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Pierre CAMI, Dec 14 2004
EXTENSIONS
Inserted 10, 40, 100, 260 - R. J. Mathar, Nov 13 2009
STATUS
approved