A084671 - OEIS

%I #20 Dec 22 2022 07:36:53

%S 5,23,67,73,157,307,389,419,449,587,661,751,1051,1229,1297,1303,1327,

%T 1823,1913,1999,2131,2179,2207,2239,2371,2689,2699,3067,3433,3593,

%U 3623,3719,3919,3943,4001,4073,4229,4241,4397,4591,4733,4919,4957,4987,5393,5449,5503

%N Primes such that the decimal concatenation of prime(n) and n is prime.

%H Michael S. Branicky, <a href="/A084671/b084671.txt">Table of n, a(n) for n = 1..10000</a>

%e 23 is a term because 23=prime(9) and concatenation of 23 and 9 is prime.

%t a=ParallelTable[Prime[k],{k,1,10^6}];k=2;Monitor[Parallelize[While[True,If[ToExpression[StringJoin[ToString/@{k,FromDigits[Position[a,k]//Flatten]}]]//PrimeQ,Print[k]];k++];k],k] (* _J.W.L. (Jan) Eerland_, Dec 22 2022 *)

%o (Python)

%o from itertools import islice

%o from sympy import isprime, sieve

%o def agen(): yield from (pn for n, pn in enumerate(sieve, 1) if isprime(int(str(pn)+str(n))))

%o print(list(islice(agen(), 52))) # _Michael S. Branicky_, Dec 22 2022

%K nonn,base

%O 1,1

%A _Zak Seidov_, Jun 29 2003

%E Edited by _Charles R Greathouse IV_, Apr 27 2010

%E a(45)-a(52) from _J.W.L. (Jan) Eerland_, Dec 22 2022