A252090 - OEIS

%I #25 Sep 08 2022 08:46:10

%S 3,13,19,31,43,61,73,79,103,109,139,151,163,199,211,223,229,241,283,

%T 331,373,421,433,439,463,541,571,613,619,631,673,691,733,769,811,829,

%U 853,859,883,919,991,1021,1033,1063,1069,1123,1153,1201,1231,1249

%N Primes p such that p + 28 is also prime.

%H Karl V. Keller, Jr., <a href="/A252090/b252090.txt">Table of n, a(n) for n = 1..10000</a>

%e 19 is in the sequence because 19 is prime and 19 + 28 = 47 is also prime.

%e 433 is in the sequence because 433 is prime and 433 + 28 = 461 is also prime.

%p P:= select(isprime, {seq(2*i+1, i=1..10000)}):

%p P intersect map(`-`,P,28);

%p # if using Maple 11 or earlier, uncomment the next line

%p # sort(convert(%,list));  # _Robert Israel_, Dec 14 2014

%t Select[Prime[Range[250]], PrimeQ[# + 28] &]

%o (Magma) [NthPrime(n): n in [1..250] | IsPrime(NthPrime(n)+28)];

%o (PARI) is(n)=isprime(n)&&isprime(n+28) \\ _Anders Hellström_, Dec 01 2015

%K nonn,easy

%O 1,1

%A _Vincenzo Librandi_, Dec 14 2014