OFFSET
1,1
COMMENTS
Indices of primes in A006567.
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
If prime(n=6)=13(1<3) and 31=prime, then 6=a(1). If prime(n=7)=17(1<7) and 71=prime, then 7=a(2). If prime(n=11)=31(3>1) and 13=prime, then 11=a(3), etc.
MATHEMATICA
difpQ[n_]:=Module[{idn=IntegerDigits[n], ridn}, ridn=Reverse[idn]; idn!=ridn && PrimeQ[FromDigits[ridn]]]; PrimePi/@ Select[ Prime[ Range[ 250]], difpQ] (* Harvey P. Dale, Nov 23 2011 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Juri-Stepan Gerasimov, Feb 16 2009
EXTENSIONS
45 replaced by 46. 127, 131, 136, 155, 159 inserted, etc. - R. J. Mathar, Feb 26 2009
STATUS
approved