|
%I #17 Sep 08 2022 08:46:14
%S 7,9,11,13,33,37,39,41,47,57,59,61,69,71,77,79,81,83,101,103,129,149,
%T 181,187,189,191,193,207,217,229,231,241,289,291,299,301,303,307,317,
%U 333,347,359,373,377,383,387,409,439,451,467,473,487,489,509,517,527
%N Numbers k such that concatenate(k,k+1,k) is prime.
%C Motivated by sequence A068660 which lists these primes.
%H Michael S. Branicky, <a href="/A264814/b264814.txt">Table of n, a(n) for n = 1..10000</a>
%e 11 is in the sequence because 111211 is prime.
%e 13 is in the sequence because 131413 is prime.
%e 15 is not in the sequence because 151615 = 5 * 30323.
%t Select[Range[800], PrimeQ[FromDigits[Join[IntegerDigits[#], IntegerDigits[# + 1], IntegerDigits[#]]]] &] (* _Alonso del Arte_, Nov 25 2015 *)
%o (PARI) is(n)=isprime(eval(Str(n,n+1,n)))
%o (Magma) [n: n in [1..700] | IsPrime(Seqint(Intseq(n) cat Intseq(n+1) cat Intseq(n)))]; // _Vincenzo Librandi_, Nov 30 2015
%o (Python)
%o from sympy import isprime
%o def aupto(N):
%o return [k for k in range(1, N+1, 2) if isprime(int(str(k)+str(k+1)+str(k)))]
%o print(aupto(530)) # _Michael S. Branicky_, Jul 09 2021
%Y Cf. A068659, A068660, A262205.
%K nonn,base
%O 1,1
%A _M. F. Hasler_, Nov 25 2015
|
