A377317 - OEIS

%I #15 Nov 10 2024 22:43:26

%S 3,4,5,7,11,13,15,18,19,25,26,36,39,49,54,55,58,69,73,102,107,110,111,

%T 116,118,129,160,164,182,184,187,194,199,206,210,218,225,229,234,236,

%U 252,253,260,271,272,275,284,285,291,300,321,339,351,352,358,387,388

%N Numbers k such that prime(k), prime(k)+6, and prime(k)+12 are primes.

%F a(n) = pi(A023241(n)).

%e 5 is in this sequence because: prime(5) = 11, and 11+6 = 17 and 11+12 = 23 are primes.

%t Select[Range[1, PrimePi[3000]], PrimeQ[Prime[#] + 6] && PrimeQ[Prime[#] + 12] &]

%o (PARI) for(k=1, primepi(3000), p = prime(k); if(isprime(p+6) && isprime(p+12), print(k)))

%Y Cf. A000040, A000720, A023241.

%Y Supersequence of A377318.

%K nonn

%O 1,1

%A _Kritsada Moomuang_, Oct 24 2024