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A380011 Beginning with 7, least prime such that the reversal concatenation of the first n terms is prime.

%I A380011 #19 Jan 18 2025 14:45:51
%S A380011 7,3,3,13,3,2,13,47,43,47,37,41,109,41,139,149,109,263,73,563,163,41,
%T A380011 19,797,61,107,31,821,43,149,37,953,211,89,547,353,337,167,67,239,
%U A380011 1009,449,97,23,349,41,31,911,61,929,229,797,331,191,463,107,463,809,2887,971
%N A380011 Beginning with 7, least prime such that the reversal concatenation of the first n terms is prime.
%C A380011 "Reverse concatenation" here refers to the decimal concatenation R(a(n)) || R(a(n-1)) || ... || R(a(3)) || R(a(2)) || R(a(1)) where R(k) means "reverse digits of k".
%H A380011 J.W.L. (Jan) Eerland, <a href="/A380011/b380011.txt">Table of n, a(n) for n = 1..982</a>
%t A380011 w={7};Do[k=1;q=Monitor[Parallelize[While[True,If[PrimeQ[FromDigits[Join@@IntegerDigits/@Reverse[IntegerDigits[FromDigits[Join@@IntegerDigits/@Append[w,Prime[k]]]]]]],Break[]];k++];Prime[k]],k];w=Append[w,q],{i,2,50}];w
%o A380011 (Python)
%o A380011 from itertools import count, islice
%o A380011 from gmpy2 import digits, is_prime, mpz, next_prime
%o A380011 def agen(): # generator of terms
%o A380011     r, an = "", 7
%o A380011     while True:
%o A380011         yield int(an)
%o A380011         r = digits(an)[::-1] + r
%o A380011         p = 2
%o A380011         while not is_prime(mpz(digits(p)[::-1]+r)): p = next_prime(p)
%o A380011         an = p
%o A380011 print(list(islice(agen(), 50))) # after _Michael S. Branicky_ in A379355
%Y A380011 Cf. A111382, A111383, A113584, A379354, A379355, A379761, A380010.
%K A380011 base,nonn
%O A380011 1,1
%A A380011 _J.W.L. (Jan) Eerland_, Jan 09 2025