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%I #23 Jan 05 2022 10:51:06
%S 53,5347,5953,6761,137131,179173,211199,223211,239233,263257,359353,
%T 541523,593587,613607,631619,653647,659653,757751,809797,977971,
%U 997991,1009997,11091103,11291123,12371231,13991381,15591553,17831777,19311913,19791973,19931987,23092297
%N Primes formed by concatenating a prime with the preceding prime.
%H K. D. Bajpai, <a href="/A088784/b088784.txt">Table of n, a(n) for n = 1..10300</a>
%e a(2) = 5347 because 5347 is 53 (a prime) concatenated with 47 (the preceding prime).
%t concatpr[n_]:=FromDigits[Join[IntegerDigits[n],IntegerDigits[ NextPrime[ n,-1]]]]; Select[concatpr/@Prime[Range[400]],PrimeQ] (* _Harvey P. Dale_, May 12 2011 *)
%o (PARI) for(n=1,10^3,p=prime(n); q=concat(Str(p),Str(precprime(p-1))); if(isprime(eval(q)), print1(q,", "))) \\ _Derek Orr_, Aug 14 2014
%o (Python)
%o from itertools import islice
%o from sympy import isprime, nextprime
%o def agen(): # generator of terms
%o p, pstr = 2, "2"
%o while True:
%o q = nextprime(p)
%o qstr = str(q)
%o t = int(qstr + pstr)
%o if isprime(t):
%o yield t
%o p, pstr = q, qstr
%o print(list(islice(agen(), 32))) # _Michael S. Branicky_, Jan 05 2022
%Y Cf. A088712.
%K base,nonn
%O 1,1
%A Chuck Seggelin (barkeep(AT)plasteredDragon.com), Oct 15 2003
%E Terms a(30), a(31) and a(32) added by _K. D. Bajpai_, Aug 14 2014
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