cp's OEIS Frontend

A309935 Primes p such that the base-10 concatenation (p+1)||p is prime.

%I A309935 #15 Sep 08 2022 08:46:22
%S A309935 3,23,41,101,107,113,179,191,197,263,269,281,293,311,353,383,389,419,
%T A309935 443,491,521,569,659,683,701,761,773,809,821,839,881,887,911,947,1109,
%U A309935 1217,1223,1229,1433,1481,1499,1559,1667,1697,1811,1901,1973,2069,2087,2099,2111,2129
%N A309935 Primes p such that the base-10 concatenation (p+1)||p is prime.
%H A309935 Robert Israel, <a href="/A309935/b309935.txt">Table of n, a(n) for n = 1..10000</a>
%e A309935 a(3) = 41 is in the sequence because 41 and 4241 are primes.
%p A309935 select(t -> isprime(t) and isprime(10^(1+ilog10(t))*(t+1)+t), [$1..20000]);
%t A309935 Select[Prime[Range[350]],PrimeQ[(#+1)10^IntegerLength[#]+#]&] (* _Harvey P. Dale_, May 07 2022 *)
%o A309935 (Magma) [p:p in PrimesUpTo(2200)| IsPrime(Seqint(Intseq(p) cat Intseq(p+1)))]; // _Marius A. Burtea_, Aug 23 2019
%o A309935 (PARI) isok(k) = isprime(k) && isprime(eval(Str(k+1, k))); \\ _Jinyuan Wang_, Aug 26 2019
%K A309935 nonn,base
%O A309935 1,1
%A A309935 _Robert Israel_, Aug 23 2019