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A118725 Chen primes for which the reversal is also a Chen prime.

%I A118725 #14 Jun 17 2020 02:08:31
%S A118725 2,3,5,7,11,13,17,31,71,101,107,113,131,149,157,167,179,181,191,199,
%T A118725 311,347,353,359,389,701,743,751,761,787,797,919,941,953,971,983,991,
%U A118725 1009,1031,1061,1091,1097,1109,1151,1217,1229,1259,1283,1301,1409,1439
%N A118725 Chen primes for which the reversal is also a Chen prime.
%H A118725 Robert Israel, <a href="/A118725/b118725.txt">Table of n, a(n) for n = 1..10000</a>
%e A118725 17 and its reversal 71 are both Chen primes.
%p A118725 revdigs:= proc(n) local L,k;
%p A118725   L:= convert(n,base,10);
%p A118725   add(L[-k]*10^(k-1),k=1..nops(L))
%p A118725 end proc:
%p A118725 filter:= proc(n) local r;
%p A118725   if not isprime(n) then return false fi;
%p A118725   r:= revdigs(n);
%p A118725   isprime(r) and numtheory:-bigomega(n+2) <= 2 and numtheory:-bigomega(r+2) <= 2
%p A118725 end proc:
%p A118725 select(filter, [2,seq(i,i=3..2000,2)]); # _Robert Israel_, Jun 16 2020
%t A118725 cpQ[n_]:=Module[{rev=FromDigits[Reverse[IntegerDigits[n]]]}, PrimeOmega[ n+2]<3 && PrimeQ[rev]&&PrimeOmega[rev+2]<3]; Select[Prime[ Range[ 400]], cpQ] (* _Harvey P. Dale_, Jul 17 2011 *)
%Y A118725 Cf. A109611.
%K A118725 base,nonn,less
%O A118725 1,1
%A A118725 Luc Stevens (lms022(AT)yahoo.com), May 21 2006
%E A118725 Corrected by _Harvey P. Dale_, Jul 17 2011