%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