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A245657 Primes p for which none of the concatenations p3, p9, 3p, 9p are primes.

%I A245657 #37 Jun 02 2025 12:52:06
%S A245657 3,107,113,179,317,443,487,599,641,653,751,773,937,977,991,1021,1087,
%T A245657 1103,1187,1201,1213,1217,1301,1409,1427,1439,1483,1553,1559,1579,
%U A245657 1609,1637,1693,1747,1777,1787,1789,1861,1949,1987,1993,2081,2129,2239,2281,2287,2293,2351,2393,2477
%N A245657 Primes p for which none of the concatenations  p3, p9, 3p, 9p are primes.
%H A245657 Harvey P. Dale, <a href="/A245657/b245657.txt">Table of n, a(n) for n = 1..10000</a>
%t A245657 Select[Prime[Range[400]],NoneTrue[{10#+3,10#+9,3*10^IntegerLength[#]+#, 9*10^IntegerLength[ #]+#},PrimeQ]&] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Sep 06 2020 *)
%o A245657 (PARI) lista(nn) = {forprime(p=2, nn, if (!isprime(eval(concat(Str(p), Str(3)))) && ! isprime(eval(concat(Str(p), Str(9)))) && ! isprime(eval(concat(Str(3), Str(p)))) && ! isprime(eval(concat(Str(9), Str(p)))), print1(p, ", ")););} \\ _Michel Marcus_, Sep 14 2014
%o A245657 (Python)
%o A245657 import sympy
%o A245657 from sympy import isprime
%o A245657 from sympy import prime
%o A245657 for n in range(1,10**3):
%o A245657   p = str(prime(n))
%o A245657   if not isprime(int(p+'3')) and not isprime(int(p+'9')) and not isprime(int('3'+p)) and not isprime(int('9'+p)):
%o A245657     print(int(p),end=', ') # _Derek Orr_, Sep 16 2014
%Y A245657 Cf. A232210, A242775, A247341, A247342.
%K A245657 nonn,base,easy
%O A245657 1,1
%A A245657 _Vladimir Shevelev_, Sep 13 2014
%E A245657 More terms from _Derek Orr_, Sep 16 2014