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

3, 107, 113, 179, 317, 443, 487, 599, 641, 653, 751, 773, 937, 977, 991, 1021, 1087, 1103, 1187, 1201, 1213, 1217, 1301, 1409, 1427, 1439, 1483, 1553, 1559, 1579, 1609, 1637, 1693, 1747, 1777, 1787, 1789, 1861, 1949, 1987, 1993, 2081, 2129, 2239, 2281, 2287, 2293, 2351, 2393, 2477

Offset: 1

Author

Vladimir Shevelev, Sep 13 2014

Keywords

• nonn
• base
• easy

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A232210, A242775, A247341, A247342.

Programs

Mathematica

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 *)

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

Python

import sympy
from sympy import isprime
from sympy import prime
for n in range(1,10**3):
  p = str(prime(n))
  if not isprime(int(p+'3')) and not isprime(int(p+'9')) and not isprime(int('3'+p)) and not isprime(int('9'+p)):
    print(int(p),end=', ') # Derek Orr, Sep 16 2014

Extensions

More terms from Derek Orr, Sep 16 2014