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A069686 Primes whose internal digits form a prime.

%I A069686 #35 Apr 20 2024 10:01:03
%S A069686 127,131,137,139,151,157,173,179,223,227,229,233,239,251,257,271,277,
%T A069686 331,337,353,359,373,379,421,431,433,439,457,479,521,523,557,571,577,
%U A069686 631,653,659,673,677,727,733,739,751,757,773,821,823,827,829,839,853
%N A069686 Primes whose internal digits form a prime.
%C A069686 Primes that remain prime upon deleting the first and last digits.
%H A069686 Jason Yuen, <a href="/A069686/b069686.txt">Table of n, a(n) for n = 1..10000</a> (correcting Christian N. K. Anderson previous bfile).
%t A069686 Select[Range[100, 853], PrimeQ[#] && PrimeQ[FromDigits[Rest[Most[IntegerDigits[#]]]]] &] (* _T. D. Noe_, Apr 05 2013 *)
%o A069686 (PARI) {indigs(n)=local(j,a,d); n=n\10; j=1; a=0; while(n>10,d=divrem(n,10); n=d[1]; a=a+j*d[2]; j=10*j); a}
%o A069686 forprime(p=1,855,if(isprime(indigs(p)),print1(p,","))) \\ _Klaus Brockhaus_, Nov 06 2002
%o A069686 (Python)
%o A069686 from sympy import isprime
%o A069686 for p in filter(isprime, range(100, 855)):
%o A069686     if isprime(int(str(p)[1:-1])): print(p) # _Jason Yuen_, Mar 28 2024
%Y A069686 Cf. A077359, A077360.
%K A069686 base,nonn,easy
%O A069686 1,1
%A A069686 _Amarnath Murthy_, Nov 05 2002
%E A069686 Edited and extended by _Klaus Brockhaus_, Nov 06 2002
%E A069686 Edited by _N. J. A. Sloane_ at the suggestion of _Andrew S. Plewe_, May 21 2007