OFFSET
1,1
COMMENTS
All terms == 0 or 1 (mod 3), and have an even number of decimal digits. - Robert Israel, May 09 2017
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
For n=12 we have 112121, which is prime.
For n=13 we have 113131, which is prime.
For n=1000 we have 1100010001, which is prime.
MAPLE
f:= n -> 1 + 1*10^(2*ilog10(n)+3)+(n)*(10+10^(2+ilog10(n))):
select(n -> isprime(f(n)), [$1..2000]); # Robert Israel, May 09 2017
MATHEMATICA
Select[Range@ 1200, PrimeQ[FromDigits@ Join[{1}, #, #, {1}]] &@ IntegerDigits[#] &] (* Michael De Vlieger, May 09 2017 *)
CROSSREFS
KEYWORD
easy,nonn,base
AUTHOR
Mark Hudson (mrmarkhudson(AT)hotmail.com), Jan 12 2005
STATUS
approved