A156793 - OEIS

%I #10 Nov 21 2013 12:49:33

%S 6,7,11,12,20,21,22,25,28,30,35,37,39,41,46,64,68,69,72,77,126,127,

%T 130,131,132,133,135,136,155,159,160,162,163,164,166,167,169,172,173,

%U 174,178,180,182,184,185,186,190,191,194,196,197,198,199,200,201,202,203

%N Indices of primes whose reversal is a different prime.

%C Indices of primes in A006567.

%H Harvey P. Dale, <a href="/A156793/b156793.txt">Table of n, a(n) for n = 1..1000</a>

%e 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.

%t 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 *)

%Y Cf. A006567.

%K nonn,base

%O 1,1

%A _Juri-Stepan Gerasimov_, Feb 16 2009

%E 45 replaced by 46. 127, 131, 136, 155, 159 inserted, etc. - _R. J. Mathar_, Feb 26 2009