%I #20 Apr 03 2023 10:36:10

%S 22,23,25,27,32,33,35,37,52,53,55,57,72,73,75,77,112,113,115,117,132,

%T 133,135,137,172,173,175,177,192,193,195,197,211,213,217,219,223,229,

%U 231,232,233,235,237,241,243,247,253,259,261,267,271,273,279,283,289

%N Numbers which are the concatenation of two primes.

%C A105184 and A121609 are subsequences.

%H T. D. Noe, <a href="/A106582/b106582.txt">Table of n, a(n) for n = 1..10000</a>

%H G. L. Honaker, Jr. and Chris Caldwell, <a href="https://t5k.org/curios/cpage/23198.html">Prime Curios! 17257</a>

%e 133 is in the sequence because 133 = 13*10+3 = A000040(6)*10+A000040(2).

%t nn=500; t=Union[Reap[Do[n=FromDigits[Join[IntegerDigits[Prime[i]], IntegerDigits[Prime[j]]]]; If[n<=nn, Sow[n]], {i,PrimePi[nn/10]}, {j,PrimePi[nn/IntegerDigits[nn][[1]]]}]][[2,1]]] (* _T. D. Noe_, Mar 11 2011 *)

%o (Python)

%o from sympy import isprime

%o from itertools import count, islice

%o def agen(): # generator of terms

%o for k in count(1):

%o s = str(k)

%o if any(s[i] != '0' and isprime(int(s[:i])) and isprime(int(s[i:])) for i in range(1, len(s))):

%o yield k

%o print(list(islice(agen(), 55))) # _Michael S. Branicky_, Feb 26 2022

%Y Cf. A001358, A105184, A121609.

%K base,nonn

%O 1,1

%A _Eric Angelini_ and _Robert G. Wilson v_, May 09 2005

%E Corrected by _Arkadiusz Wesolowski_, Mar 11 2011