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A345346 Primes whose digit reversal is twice a prime.

%I A345346 #23 Jun 17 2021 06:04:43
%S A345346 41,43,47,83,229,241,263,283,419,431,433,439,479,491,601,607,641,643,
%T A345346 647,661,683,811,853,857,859,877,2039,2063,2069,2083,2099,2203,2207,
%U A345346 2251,2273,2281,2287,2411,2417,2423,2437,2467,2473,2617,2621,2663,2671,2677,2683,2687,2689,2801,2819,2837
%N A345346 Primes whose digit reversal is twice a prime.
%H A345346 Karl-Heinz Hofmann, <a href="/A345346/b345346.txt">Table of n, a(n) for n = 1..10000</a>
%e A345346 a(3) = 47 is a term because 47 and 74/2 = 37 are primes.
%p A345346 revdigs:= proc(n) local L,i;
%p A345346   L:= convert(n,base,10);
%p A345346   add(L[-i]*10^(i-1),i=1..nops(L))
%p A345346 end proc:
%p A345346 filter:= proc(n) isprime(n) and numtheory:-bigomega(revdigs(n))=2 end proc:
%p A345346 select(filter, [seq(seq(seq(i*10^d+j,j=1..10^d-1,2),i=2..8,2),d=1..4)]);
%o A345346 (PARI) isok(p) = if (isprime(p), my(r=fromdigits(Vecrev(digits(p)))); if (!(r%2), isprime(r/2))); \\ _Michel Marcus_, Jun 15 2021
%o A345346 (Python) from sympy import isprime, primerange
%o A345346 def ok(p): t = int(str(p)[::-1]); return t%2 == 0 and isprime(t//2)
%o A345346 print(list(filter(ok, primerange(1, 2838)))) # _Michael S. Branicky_, Jun 16 2021
%Y A345346 Intersection of A085778 and A273892.
%K A345346 nonn,base
%O A345346 1,1
%A A345346 _J. M. Bergot_ and _Robert Israel_, Jun 14 2021