1,2

Some of the larger entries may only correspond to probable primes.

There cannot be any primes of this form when n is even, because all such numbers must be divisible by 11. A number is divisible by 11 if the difference between the sum of its odd digits and the sum of its even digits is 0 or divisible by 11. When n is even the difference is always 0. - Dmitry Kamenetsky (dkamen(AT)rsise.anu.edu.au), Jul 12 2008

For n=3 we have 10^3+21 = 1000+21 = 1021, which is prime.

q=21; s=""; For[ a=q, a<=q, s="10^n+"<>ToString[ a ]<>":"; n=0; For[ i=1, i< 10^3, If[ PrimeQ[ 10^i+a ], n=1; s=s<>ToString[ i ]<>", " ]; i++ ]; If[ n>0, Print[ s ] ]; a++ ] - Vladimir Orlovsky, May 06 2008

Cf. A049054, A088274, A088275.

Sequence in context: A011755 A128301 A018307 this_sequence A009211 A105538 A056404

Adjacent sequences: A108047 A108048 A108049 this_sequence A108051 A108052 A108053

hard,more,nonn

Julien Peter Benney (jpbenney(AT)ftml.net), Jun 01 2005

Corrected by Vladimir Orlovsky, May 06 2008

a(10)-a(13) from Dmitry Kamenetsky (dkamen(AT)rsise.anu.edu.au), Jul 12 2008