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%I #15 Jun 23 2018 07:21:51
%S 23,37,53,73,113,137,173,193,197,211,223,227,229,233,241,257,271,277,
%T 283,293,311,313,317,331,337,347,353,359,367,373,379,383,389,397,433,
%U 523,541,547,557,571,577,593,613,617,673,677,719,727,733,743,757,761,773,797,977
%N Primes formed by concatenating other primes.
%H M. F. Hasler, <a href="/A019549/b019549.txt">Table of n, a(n) for n = 1..17495</a>
%H Sylvester Smith, <a href="https://www.gallup.unm.edu/~smarandache/SYLSMITH.HTM">A Set of Conjectures on Smarandache Sequences</a>, Bulletin of Pure and Applied Sciences, (Bombay, India), Vol. 15 E (No. 1), 1996, pp. 101-107.
%e 113 is member as 11 and 3 are primes.
%e a(12)=227 = "2"+"2"+"7" is the first term not in A105184 (restricted to concatenation of two primes). [_M. F. Hasler_, Oct 15 2009]
%o (PARI) is_A019549(n, recurse=0)={ isprime(n) == recurse & return(recurse); for(i=1, #Str(n)-1, isprime( n%10^i ) & is_A019549( n\10^i, 1) & n\10^(i-1)%10 & return(1)) } \\ _M. F. Hasler_, Oct 15 2009
%Y Cf. A105184, A152242.
%K nonn,base
%O 1,1
%A R. Muller
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