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) =53 because (i) 53 is prime and (ii) when 53 is concatenated with its reverse (35) - 2, the result (5333) is prime.
MATHEMATICA
Select[Prime[Range[600]], PrimeQ[FromDigits[Join[IntegerDigits[#], Reverse[ IntegerDigits[ #]]]]- 2]&] (* Harvey P. Dale, Apr 06 2017 *)
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Chuck Seggelin (barkeep(AT)plastereddragon.com), Oct 21 2003
STATUS
approved