A225581 - OEIS

%I #36 Sep 07 2021 19:49:37

%S 3,5,3,3,3,5,3,3,7,5,3,3,3,5,3,7,3,11,3,5,5,5,5,3,5,11,17,3,3,5,47,11,

%T 5,5,3,3,3,5,13,11,3,3,5,5,5,11,11,11,3,3,7,5,3,5,3,5,5,3,5,13,11,7,3,

%U 5,11,5,3,5,5,3,19,3,3,5,29,17,3,23,3,5,7,5,5,71,3,5,5,3,3,47,3,5,3,11,3,5,3,3,11,5,23

%N a(n) is the minimal odd prime q such that prime(n)*q + prime(n) + q is prime.

%H John-Å. W. Olsen, <a href="/A225581/b225581.txt">Table of n, a(n) for n = 1..1000</a>

%e n = 1;  p = 2;  q = 3;

%e n = 2;  p = 3;  q = 5;

%e n = 3;  p = 5;  q = 3;

%e n = 4;  p = 7;  q = 3;

%t a[n_] := Block[{q = 3, p = Prime@n},While[! PrimeQ[p*q + p + q], q = NextPrime@q]; q]; Array[a, 101] (* _Giovanni Resta_, May 11 2013 *)

%o (PARI) a(n) = my(q=3, p=prime(n)); while(!isprime(p*q+p+q), q = nextprime(q+1)); q; \\ _Michel Marcus_, Sep 06 2021

%o (Python)

%o from sympy import isprime, nextprime, prime

%o def a(n):

%o     q, p = 3, prime(n)

%o     while not isprime(p*q + p + q): q = nextprime(q)

%o     return q

%o print([a(n) for n in range(1, 102)]) # _Michael S. Branicky_, Sep 06 2021

%Y Cf. A000040.

%K nonn,easy

%O 1,1

%A _John-Å. W. Olsen_, May 11 2013