OFFSET
1,1
EXAMPLE
13, 17, 31, 37, 71, 73, 79 and 97 are reversible primes (emirps), so a(2)=8.
MATHEMATICA
emrpQ[n_]:=Module[{idn=IntegerDigits[n], rev}, rev=Reverse[idn]; rev!=idn && Max[DigitCount[n]] ==1&&PrimeQ[FromDigits[rev]]]; With[{ems=Select[ Prime[ Range[ 51*10^6]], emrpQ]}, Join[ {4}, Table[Count[ems, _?(IntegerLength[ #] == n&)], {n, 2, 9}]]] (* Harvey P. Dale, Nov 29 2014 *)
PROG
(Python)
from sympy import primerange, isprime
def A003684(n):
return len([p for p in primerange(10**(n-1), 10**n)
if len(set(str(p))) == len(str(p)) and isprime(int(str(p)[::-1]))])
# Chai Wah Wu, Aug 14 2014
CROSSREFS
KEYWORD
nonn,fini,full,base,easy,nice
AUTHOR
EXTENSIONS
Typo in example corrected by David Ritterskamp (dritters(AT)usi.edu), Mar 24 2008
STATUS
approved