OFFSET
1,1
COMMENTS
It appears that if concat(p,reverse(p))+2 is prime, then concat(p,reverse(p))-2 is not and vice versa. This was tested for the first 60000 primes.
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
a(4) =109 because (i) 109 is prime and (ii) when 109 is concatenated with its reverse (901) + 2, the result (109903) is prime.
MATHEMATICA
crpQ[n_]:=Module[{idn=IntegerDigits[n]}, PrimeQ[FromDigits[ Join[ idn, Reverse[ idn]]]+2]]; Select[Prime[Range[1000]], crpQ] (* Harvey P. Dale, Apr 28 2014 *)
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Chuck Seggelin (barkeep(AT)plastereddragon.com), Oct 21 2003
STATUS
approved