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%I #20 Apr 09 2022 09:31:00
%S 3,9,19,21,37,63,77,81,87,107,121,133,177,201,211,213,217,281,293,303,
%T 321,327,329,333,351,391,393,439,481,503,507,519,543,547,551,561,579,
%U 581,599,621,639,657,663,667,711,721,727,743,793,813,819,827,829,831,837
%N Numbers k such that concatenation of prime(k) and k is prime.
%H Harvey P. Dale, <a href="/A084670/b084670.txt">Table of n, a(n) for n = 1..1000</a>
%e 9 is a term because prime(9) = 23 and concatenation of 23 and 9 is prime
%t Select[Range[1000],PrimeQ[Prime[#]10^IntegerLength[#]+#]&] (* _Harvey P. Dale_, Apr 09 2022 *)
%o (PARI) is(k) = ispseudoprime(eval(Str(prime(k), k))); \\ _Jinyuan Wang_, Apr 10 2020
%o (Python)
%o from sympy import isprime, prime
%o def aupto(lim):
%o return [k for k in range(1, lim+1) if isprime(int(str(prime(k))+str(k)))]
%o print(aupto(837)) # _Michael S. Branicky_, Mar 09 2021
%Y Cf. A075110, A084669.
%K nonn,base
%O 1,1
%A _Zak Seidov_, Jun 29 2003
%E More terms from _Jinyuan Wang_, Apr 10 2020
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