Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #31 Sep 06 2020 13:08:23
%S 3,107,113,179,317,443,487,599,641,653,751,773,937,977,991,1021,1087,
%T 1103,1187,1201,1213,1217,1301,1409,1427,1439,1483,1553,1559,1579,
%U 1609,1637,1693,1747,1777,1787,1789,1861,1949,1987,1993,2081,2129,2239,2281,2287,2293,2351,2393,2477
%N Primes p for which none of the concatenations p3, p9, 3p, 9p are primes.
%H Harvey P. Dale, <a href="/A245657/b245657.txt">Table of n, a(n) for n = 1..10000</a>
%t 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 (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 (Python)
%o import sympy
%o from sympy import isprime
%o from sympy import prime
%o for n in range(1,10**3):
%o ..p = str(prime(n))
%o ..if not isprime(p+'3') and not isprime(p+'9') and not isprime('3'+p) and not isprime('9'+p):
%o ....print(int(p),end=', ') # _Derek Orr_, Sep 16 2014
%Y Cf. A232210, A242775, A247341, A247342.
%K nonn,base,easy
%O 1,1
%A _Vladimir Shevelev_, Sep 13 2014
%E More terms from _Derek Orr_, Sep 16 2014