OFFSET
1,1
LINKS
Pierre CAMI, Table of n, a(n) for n = 1..10000
EXAMPLE
343 is composite, 545 is composite, 747 is composite, 11411 is prime so a(1)=11.
MATHEMATICA
Select[Prime[Range[300]], PrimeQ[FromDigits[Join[IntegerDigits[#], {4}, IntegerDigits[ #]]]]&] (* Harvey P. Dale, Aug 01 2016 *)
PROG
(PFGW & SCRIPT), the pre10.txt file with the first 10000000 prime numbers.
SCRIPT
DIM i, 0
DIM j
DIM k
DIM n, 1
OPENFILEOUT myf, a(n).txt
OPENFILEIN maf, pre10.txt
GETNEXT j, maf
LABEL loop1
GETNEXT j, maf
IF j>10^n THEN SET n, n+1
SET k, j*10^(n+1)+4*10^n+j
PRP k
IF ISPRP THEN GOTO w
GOTO loop1
LABEL w
SET i, i+1
WRITE myf, j
IF i>9999 THEN END
GOTO loop1
(PARI) lista(nn) = {forprime(p=1, nn, if (isprime(eval(concat(concat(Str(p), 4), Str(p)))), print1(p, ", ")); ); } \\ Michel Marcus, Oct 27 2014
(Magma) [p: p in PrimesUpTo(3000) | IsPrime(Seqint(Intseq(p) cat [4] cat Intseq(p)))]; // Vincenzo Librandi, Oct 27 2014
(Python)
from sympy import isprime, primerange
def ok(p): s = str(p); return isprime(int(s + "4" + s))
def aupto(limit): return [p for p in primerange(1, limit+1) if ok(p)]
print(aupto(2700)) # Michael S. Branicky, Nov 17 2021
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Pierre CAMI, Oct 27 2014
STATUS
approved